// Copyright (c) Microsoft Open Technologies, Inc. All rights reserved. See License.txt in the project root for license information.

namespace System.Data.Entity.SqlServer.SqlGen
{
    using System.Collections.Generic;
    using System.Data.Entity.Core.Common;
    using System.Data.Entity.Core.Common.CommandTrees;
    using System.Data.Entity.Core.Common.CommandTrees.ExpressionBuilder;
    using System.Data.Entity.Core.Common.CommandTrees.ExpressionBuilder.Spatial;
    using System.Data.Entity.Core.Metadata.Edm;
    using System.Data.Entity.Spatial;
    using System.Data.Entity.SqlServer.Resources;
    using System.Data.Entity.SqlServer.Utilities;
    using System.Data.SqlClient;
    using System.Diagnostics;
    using System.Diagnostics.CodeAnalysis;
    using System.Globalization;
    using System.Linq;
    using System.Text;

    // <summary>
    // Translates the command object into a SQL string that can be executed on
    // SQL Server 2000 and SQL Server 2005.
    // </summary>
    // <remarks>
    // The translation is implemented as a visitor <see cref="DbExpressionVisitor{TResultType}" />
    // over the query tree.  It makes a single pass over the tree, collecting the sql
    // fragments for the various nodes in the tree <see cref="ISqlFragment" />.
    // The major operations are
    // <list type="bullet">
    //     <item>
    //         Select statement minimization.  Multiple nodes in the query tree
    //         that can be part of a single SQL select statement are merged. e.g. a
    //         Filter node that is the input of a Project node can typically share the
    //         same SQL statement.
    //     </item>
    //     <item>
    //         Alpha-renaming.  As a result of the statement minimization above, there
    //         could be name collisions when using correlated subqueries
    //         <example>
    //             <code>Filter(
    //                 b = Project( c.x
    //                 c = Extent(xyz)
    //                 )
    //                 exists (
    //                 Filter(
    //                 c = Extent(xyz)
    //                 b.x = c.x
    //                 )
    //                 )
    //                 )</code>
    //             The first Filter, Project and Extent will share the same SQL select statement.
    //             The alias for the Project i.e. b, will be replaced with c.
    //             If the alias c for the Filter within the exists clause is not renamed,
    //             we will get <c>c.x = c.x</c>, which is incorrect.
    //             Instead, the alias c within the second filter should be renamed to c1, to give
    //             <c>c.x = c1.x</c> i.e. b is renamed to c, and c is renamed to c1.
    //         </example>
    //     </item>
    //     <item>
    //         Join flattening.  In the query tree, a list of join nodes is typically
    //         represented as a tree of Join nodes, each with 2 children. e.g.
    //         <example>
    //             <code>a = Join(InnerJoin
    //                 b = Join(CrossJoin
    //                 c = Extent(xyz)
    //                 d = Extent(xyz)
    //                 )
    //                 e = Extent(xyz)
    //                 on b.c.x = e.x
    //                 )</code>
    //             If translated directly, this will be translated to
    //             <code>FROM ( SELECT c.*, d.*
    //                 FROM xyz as c
    //                 CROSS JOIN xyz as d) as b
    //                 INNER JOIN xyz as e on b.x' = e.x</code>
    //             It would be better to translate this as
    //             <code>FROM xyz as c
    //                 CROSS JOIN xyz as d
    //                 INNER JOIN xyz as e on c.x = e.x</code>
    //             This allows the optimizer to choose an appropriate join ordering for evaluation.
    //         </example>
    //     </item>
    //     <item>
    //         Select * and column renaming.  In the example above, we noticed that
    //         in some cases we add
    //         <c>SELECT * FROM ...</c>
    //         to complete the SQL
    //         statement. i.e. there is no explicit PROJECT list.
    //         In this case, we enumerate all the columns available in the FROM clause
    //         This is particularly problematic in the case of Join trees, since the columns
    //         from the extents joined might have the same name - this is illegal.  To solve
    //         this problem, we will have to rename columns if they are part of a SELECT *
    //         for a JOIN node - we do not need renaming in any other situation.
    //         <see cref="SqlGenerator.AddDefaultColumns" />
    //         .
    //     </item>
    // </list>
    // <para> Renaming issues. When rows or columns are renamed, we produce names that are unique globally with respect to the query. The names are derived from the original names, with an integer as a suffix. e.g. CustomerId will be renamed to CustomerId1, CustomerId2 etc. Since the names generated are globally unique, they will not conflict when the columns of a JOIN SELECT statement are joined with another JOIN. </para>
    // <para>
    //     Record flattening. SQL server does not have the concept of records. However, a join statement produces records. We have to flatten the record accesses into a simple <c>alias.column</c> form.
    //     <see
    //         cref="SqlGenerator.Visit(DbPropertyExpression)" />
    // </para>
    // <para>
    //     Building the SQL. There are 2 phases
    //     <list type="numbered">
    //         <item>
    //             Traverse the tree, producing a sql builder
    //             <see cref="SqlBuilder" />
    //         </item>
    //         <item>
    //             Write the SqlBuilder into a string, renaming the aliases and columns
    //             as needed.
    //         </item>
    //     </list>
    //     In the first phase, we traverse the tree. We cannot generate the SQL string right away, since
    //     <list
    //         type="bullet">
    //         <item>The WHERE clause has to be visited before the from clause.</item>
    //         <item>
    //             extent aliases and column aliases need to be renamed.  To minimize
    //             renaming collisions, all the names used must be known, before any renaming
    //             choice is made.
    //         </item>
    //     </list>
    //     To defer the renaming choices, we use symbols
    //     <see
    //         cref="Symbol" />
    //     . These are renamed in the second phase. Since visitor methods cannot transfer information to child nodes through parameters, we use some global stacks,
    //     <list
    //         type="bullet">
    //         <item>
    //             A stack for the current SQL select statement.  This is needed by
    //             <see cref="SqlGenerator.Visit(DbVariableReferenceExpression)" />
    //             to create a
    //             list of free variables used by a select statement.  This is needed for
    //             alias renaming.
    //         </item>
    //         <item>
    //             A stack for the join context.  When visiting an extent,
    //             we need to know whether we are inside a join or not.  If we are inside
    //             a join, we do not create a new SELECT statement.
    //         </item>
    //     </list>
    // </para>
    // <para>
    //     Global state. To enable renaming, we maintain
    //     <list type="bullet">
    //         <item>The set of all extent aliases used.</item>
    //         <item>The set of all parameter names.</item>
    //         <item>The set of all column names that may need to be renamed.</item>
    //     </list>
    //     Finally, we have a symbol table to lookup variable references. All references to the same extent have the same symbol.
    // </para>
    // <para>
    //     Sql select statement sharing. Each of the relational operator nodes
    //     <list type="bullet">
    //         <item>Project</item>
    //         <item>Filter</item>
    //         <item>GroupBy</item>
    //         <item>Sort/OrderBy</item>
    //     </list>
    //     can add its non-input (e.g. project, predicate, sort order etc.) to the SQL statement for the input, or create a new SQL statement. If it chooses to reuse the input's SQL statement, we play the following symbol table trick to accomplish renaming. The symbol table entry for the alias of the current node points to the symbol for the input in the input's SQL statement.
    //     <example>
    //         <code>Project(b.x
    //             b = Filter(
    //             c = Extent(xyz)
    //             c.x = 5)
    //             )</code>
    //         The Extent node creates a new SqlSelectStatement.  This is added to the
    //         symbol table by the Filter as {c, Symbol(c)}.  Thus, <c>c.x</c> is resolved to
    //         <c>Symbol(c).x</c>.
    //         Looking at the project node, we add {b, Symbol(c)} to the symbol table if the
    //         SQL statement is reused, and {b, Symbol(b)}, if there is no reuse.
    //         Thus, <c>b.x</c> is resolved to <c>Symbol(c).x</c> if there is reuse, and to
    //         <c>Symbol(b).x</c> if there is no reuse.
    //     </example>
    // </para>
    // </remarks>
    [SuppressMessage("Microsoft.Maintainability", "CA1506:AvoidExcessiveClassCoupling")]
    internal class SqlGenerator : DbExpressionVisitor<ISqlFragment>
    {
        // <summary>
        // Every relational node has to pass its SELECT statement to its children
        // This allows them (DbVariableReferenceExpression eventually) to update the list of
        // outer extents (free variables) used by this select statement.
        // </summary>
        private Stack<SqlSelectStatement> selectStatementStack;

        // <summary>
        // The top of the stack
        // </summary>
        private SqlSelectStatement CurrentSelectStatement
        {
            // There is always something on the stack, so we can always Peek.
            get { return selectStatementStack.Peek(); }
        }

        // <summary>
        // Nested joins and extents need to know whether they should create
        // a new Select statement, or reuse the parent's.  This flag
        // indicates whether the parent is a join or not.
        // </summary>
        private Stack<bool> isParentAJoinStack;

        // <summary>
        // Determine if the parent is a join.
        // </summary>
        private bool IsParentAJoin
        {
            // There might be no entry on the stack if a Join node has never
            // been seen, so we return false in that case.
            get { return isParentAJoinStack.Count != 0 && isParentAJoinStack.Peek(); }
        }

        private Dictionary<string, int> allExtentNames;

        internal Dictionary<string, int> AllExtentNames
        {
            get { return allExtentNames; }
        }

        // For each column name, we store the last integer suffix that
        // was added to produce a unique column name.  This speeds up
        // the creation of the next unique name for this column name.
        private Dictionary<string, int> allColumnNames;

        internal Dictionary<string, int> AllColumnNames
        {
            get { return allColumnNames; }
        }

        private readonly SymbolTable symbolTable = new SymbolTable();

        // <summary>
        // VariableReferenceExpressions are allowed only as children of DbPropertyExpression
        // or MethodExpression.  The cheapest way to ensure this is to set the following
        // property in DbVariableReferenceExpression and reset it in the allowed parent expressions.
        // </summary>
        private bool isVarRefSingle;

        private readonly SymbolUsageManager optionalColumnUsageManager = new SymbolUsageManager();

        // <summary>
        // Maintain the list of (string) DbParameterReferenceExpressions that should be compensated, viz.
        // forced to non-unicode format. A parameter is added to the list if it is being compared to a
        // non-unicode store column and none of its other usages in the query tree, disqualify it
        // (For example - if the parameter is also being projected or compared to a unicode column)
        // The goal of the compensation is to have the store index picked up by the server.
        // String constants are also compensated and the decision is local, unlike parameters.
        // </summary>
        private readonly Dictionary<string, bool> _candidateParametersToForceNonUnicode = new Dictionary<string, bool>();

        // <summary>
        // Set and reset in DbComparisonExpression and DbLikeExpression visit methods. Maintains
        // global state information that the children of these nodes are candidates for compensation.
        // </summary>
        private bool _forceNonUnicode;

        // <summary>
        // Set when it is is safe to ignore the unicode/non-unicode aspect. See <see cref="VisitIsNullExpression" /> for an example.
        // </summary>
        private bool _ignoreForceNonUnicodeFlag;

        private const byte DefaultDecimalPrecision = 18;
        private static readonly char[] _hexDigits = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F' };

        private List<string> _targets;

        public List<string> Targets
        {
            get { return _targets; }
        }

        // Define lists of functions that take string arugments and return strings.
        private static readonly ISet<string> _canonicalAndStoreStringFunctionsOneArg =
            new HashSet<string>(StringComparer.Ordinal)
                {
                    "Edm.Trim",
                    "Edm.RTrim",
                    "Edm.LTrim",
                    "Edm.Left",
                    "Edm.Right",
                    "Edm.Substring",
                    "Edm.ToLower",
                    "Edm.ToUpper",
                    "Edm.Reverse",
                    "SqlServer.RTRIM",
                    "SqlServer.LTRIM",
                    "SqlServer.LEFT",
                    "SqlServer.RIGHT",
                    "SqlServer.SUBSTRING",
                    "SqlServer.LOWER",
                    "SqlServer.UPPER",
                    "SqlServer.REVERSE"
                };

        // <summary>
        // The current SQL Server version
        // </summary>
        private readonly SqlVersion _sqlVersion;

        internal SqlVersion SqlVersion
        {
            get { return _sqlVersion; }
        }

        internal bool IsPreKatmai
        {
            get { return SqlVersionUtils.IsPreKatmai(SqlVersion); }
        }

        private TypeUsage _integerType;

        internal TypeUsage IntegerType
        {
            get
            {
                return _integerType
                       ?? (_integerType = TypeUsage.CreateDefaultTypeUsage(
                           StoreItemCollection.GetPrimitiveTypes().First(t => t.PrimitiveTypeKind == PrimitiveTypeKind.Int64)));
            }
        }

        private StoreItemCollection _storeItemCollection;

        internal virtual StoreItemCollection StoreItemCollection
        {
            get { return _storeItemCollection; }
        }

        internal SqlGenerator()
        {
            // Testing only

            _sqlVersion = SqlVersion.Sql11;
        }

        // <summary>
        // Basic constructor.
        // </summary>
        // <param name="sqlVersion"> server version </param>
        internal SqlGenerator(SqlVersion sqlVersion)
        {
            _sqlVersion = sqlVersion;
        }

        // <summary>
        // General purpose static function that can be called from System.Data assembly
        // </summary>
        // <param name="tree"> command tree </param>
        // <param name="sqlVersion"> Server version </param>
        // <param name="parameters"> Parameters to add to the command tree corresponding to constants in the command tree. Used only in ModificationCommandTrees. </param>
        // <param name="commandType"> CommandType for generated command. </param>
        // <returns> The string representing the SQL to be executed. </returns>
        internal static string GenerateSql(
            DbCommandTree tree, SqlVersion sqlVersion, out List<SqlParameter> parameters, out CommandType commandType,
            out HashSet<string> paramsToForceNonUnicode)
        {
            commandType = CommandType.Text;
            parameters = null;
            paramsToForceNonUnicode = null;

            var sqlGenerator = new SqlGenerator(sqlVersion);

            switch (tree.CommandTreeKind)
            {
                case DbCommandTreeKind.Query:
                    return sqlGenerator.GenerateSql((DbQueryCommandTree)tree, out paramsToForceNonUnicode);

                case DbCommandTreeKind.Insert:
                    return DmlSqlGenerator.GenerateInsertSql((DbInsertCommandTree)tree, sqlGenerator, out parameters);

                case DbCommandTreeKind.Delete:
                    return DmlSqlGenerator.GenerateDeleteSql((DbDeleteCommandTree)tree, sqlGenerator, out parameters);

                case DbCommandTreeKind.Update:
                    return DmlSqlGenerator.GenerateUpdateSql((DbUpdateCommandTree)tree, sqlGenerator, out parameters);

                case DbCommandTreeKind.Function:
                    return GenerateFunctionSql((DbFunctionCommandTree)tree, out commandType);

                default:
                    //We have covered all command tree kinds
                    Debug.Assert(false, "Unknown command tree kind");
                    return null;
            }
        }

        private static string GenerateFunctionSql(DbFunctionCommandTree tree, out CommandType commandType)
        {
            DebugCheck.NotNull(tree.EdmFunction);

            var function = tree.EdmFunction;

            if (String.IsNullOrEmpty(function.CommandTextAttribute))
            {
                // build a quoted description of the function
                commandType = CommandType.StoredProcedure;

                // if the schema name is not explicitly given, it is assumed to be the metadata namespace
                var schemaName = String.IsNullOrEmpty(function.Schema)
                                     ? function.NamespaceName
                                     : function.Schema;

                // if the function store name is not explicitly given, it is assumed to be the metadata name
                var functionName = String.IsNullOrEmpty(function.StoreFunctionNameAttribute)
                                       ? function.Name
                                       : function.StoreFunctionNameAttribute;

                // quote elements of function text
                var quotedSchemaName = QuoteIdentifier(schemaName);
                var quotedFunctionName = QuoteIdentifier(functionName);

                // separator
                const string schemaSeparator = ".";

                // concatenate elements of function text
                var quotedFunctionText = quotedSchemaName + schemaSeparator + quotedFunctionName;

                return quotedFunctionText;
            }
            else
            {
                // if the user has specified the command text, pass it through verbatim and choose CommandType.Text
                commandType = CommandType.Text;
                return function.CommandTextAttribute;
            }
        }

        // <summary>
        // Translate a command tree to a SQL string.
        // The input tree could be translated to either a SQL SELECT statement
        // or a SELECT expression.  This choice is made based on the return type
        // of the expression
        // CollectionType => select statement
        // non collection type => select expression
        // </summary>
        // <returns> The string representing the SQL to be executed. </returns>
        internal string GenerateSql(DbQueryCommandTree tree, out HashSet<string> paramsToForceNonUnicode)
        {
            DebugCheck.NotNull(tree.Query);

            _targets = new List<string>();

            var targetTree = tree;

            //If we are on Sql 8.0 rewrite the tree if needed
            if (SqlVersion == SqlVersion.Sql8)
            {
                if (Sql8ConformanceChecker.NeedsRewrite(tree.Query))
                {
                    targetTree = Sql8ExpressionRewriter.Rewrite(tree);
                }
            }

            // needed in Private Type Helpers section bellow
            _storeItemCollection = (StoreItemCollection)targetTree.MetadataWorkspace.GetItemCollection(DataSpace.SSpace);

            selectStatementStack = new Stack<SqlSelectStatement>();
            isParentAJoinStack = new Stack<bool>();

            allExtentNames = new Dictionary<string, int>(StringComparer.OrdinalIgnoreCase);
            allColumnNames = new Dictionary<string, int>(StringComparer.OrdinalIgnoreCase);

            // Literals will not be converted to parameters.

            ISqlFragment result;

            if (BuiltInTypeKind.CollectionType == targetTree.Query.ResultType.EdmType.BuiltInTypeKind)
            {
                var sqlStatement = VisitExpressionEnsureSqlStatement(targetTree.Query);

                Debug.Assert(sqlStatement != null, "The outer most sql statment is null");

                sqlStatement.IsTopMost = true;
                result = sqlStatement;
            }
            else
            {
                var sqlBuilder = new SqlBuilder();

                sqlBuilder.Append("SELECT ");
                sqlBuilder.Append(targetTree.Query.Accept(this));

                result = sqlBuilder;
            }

            if (isVarRefSingle)
            {
                throw new NotSupportedException();
                // A DbVariableReferenceExpression has to be a child of DbPropertyExpression or MethodExpression
            }

            // Check that the parameter stacks are not leaking.
            Debug.Assert(selectStatementStack.Count == 0);
            Debug.Assert(isParentAJoinStack.Count == 0);

            paramsToForceNonUnicode =
                new HashSet<string>(_candidateParametersToForceNonUnicode.Where(p => p.Value).Select(q => q.Key).ToList());

            var builder = new StringBuilder(1024);
            using (var writer = new SqlWriter(builder))
            {
                WriteSql(writer, result);
            }

            return builder.ToString();
        }

        // <summary>
        // Convert the SQL fragments to a string. Writes a string representing the SQL to be executed
        // into the specified writer.
        // </summary>
        // <param name="sqlStatement">The fragment to be emitted</param>
        // <returns>The writer specified for fluent continuations. </returns>
        internal SqlWriter WriteSql(SqlWriter writer, ISqlFragment sqlStatement)
        {
            sqlStatement.WriteSql(writer, this);
            return writer;
        }

        // <summary>
        // Translate(left) AND Translate(right)
        // </summary>
        // <returns>
        // A <see cref="SqlBuilder" /> .
        // </returns>
        public override ISqlFragment Visit(DbAndExpression e)
        {
            Check.NotNull(e, "e");

            return VisitBinaryExpression(" AND ", DbExpressionKind.And, e.Left, e.Right);
        }

        // <summary>
        // An apply is just like a join, so it shares the common join processing
        // in <see cref="VisitJoinExpression" />
        // </summary>
        // <returns>
        // A <see cref="SqlSelectStatement" /> .
        // </returns>
        public override ISqlFragment Visit(DbApplyExpression e)
        {
            Check.NotNull(e, "e");

            Debug.Assert(SqlVersion != SqlVersion.Sql8, "DbApplyExpression when translating for SQL Server 2000.");

            var inputs = new List<DbExpressionBinding>();
            inputs.Add(e.Input);
            inputs.Add(e.Apply);

            string joinString;
            switch (e.ExpressionKind)
            {
                case DbExpressionKind.CrossApply:
                    joinString = "CROSS APPLY";
                    break;

                case DbExpressionKind.OuterApply:
                    joinString = "OUTER APPLY";
                    break;

                default:
                    Debug.Assert(false);
                    throw new InvalidOperationException(String.Empty);
            }

            // The join condition does not exist in this case, so we use null.
            // WE do not have a on clause, so we use JoinType.CrossJoin.
            return VisitJoinExpression(inputs, DbExpressionKind.CrossJoin, joinString, null);
        }

        // <summary>
        // For binary expressions, we delegate to <see cref="VisitBinaryExpression" />.
        // We handle the other expressions directly.
        // </summary>
        // <returns>
        // A <see cref="SqlBuilder" />
        // </returns>
        public override ISqlFragment Visit(DbArithmeticExpression e)
        {
            Check.NotNull(e, "e");

            SqlBuilder result;

            switch (e.ExpressionKind)
            {
                case DbExpressionKind.Divide:
                    result = VisitBinaryExpression(" / ", e.ExpressionKind, e.Arguments[0], e.Arguments[1]);
                    break;
                case DbExpressionKind.Minus:
                    result = VisitBinaryExpression(" - ", e.ExpressionKind, e.Arguments[0], e.Arguments[1]);
                    break;
                case DbExpressionKind.Modulo:
                    result = VisitBinaryExpression(" % ", e.ExpressionKind, e.Arguments[0], e.Arguments[1]);
                    break;
                case DbExpressionKind.Multiply:
                    result = VisitBinaryExpression(" * ", e.ExpressionKind, e.Arguments[0], e.Arguments[1]);
                    break;
                case DbExpressionKind.Plus:
                    result = VisitBinaryExpression(" + ", e.ExpressionKind, e.Arguments[0], e.Arguments[1]);
                    break;

                case DbExpressionKind.UnaryMinus:
                    result = new SqlBuilder();
                    result.Append(" -(");
                    result.Append(e.Arguments[0].Accept(this));
                    result.Append(")");
                    break;

                default:
                    Debug.Assert(false);
                    throw new InvalidOperationException(String.Empty);
            }

            return result;
        }

        // <summary>
        // If the ELSE clause is null, we do not write it out.
        // </summary>
        // <returns>
        // A <see cref="SqlBuilder" />
        // </returns>
        public override ISqlFragment Visit(DbCaseExpression e)
        {
            Check.NotNull(e, "e");

            var result = new SqlBuilder();

            Debug.Assert(e.When.Count == e.Then.Count);

            result.Append("CASE");
            for (var i = 0; i < e.When.Count; ++i)
            {
                result.Append(" WHEN (");
                result.Append(e.When[i].Accept(this));
                result.Append(") THEN ");
                result.Append(e.Then[i].Accept(this));
            }
            // REVIEW: e.Else = DbNullExpression is added by the parser if there is
            // no else clause.  So, we do not add an ELSE clause here.
            if (e.Else != null
                && !(e.Else is DbNullExpression))
            {
                result.Append(" ELSE ");
                result.Append(e.Else.Accept(this));
            }

            result.Append(" END");

            return result;
        }

        public override ISqlFragment Visit(DbCastExpression e)
        {
            Check.NotNull(e, "e");

            if (e.ResultType.IsSpatialType())
            {
                return e.Argument.Accept(this);
            }
            else
            {
                var result = new SqlBuilder();
                result.Append(" CAST( ");
                result.Append(e.Argument.Accept(this));
                result.Append(" AS ");
                result.Append(GetSqlPrimitiveType(e.ResultType));
                result.Append(")");

                return result;
            }
        }

        // <summary>
        // The parser generates Not(Equals(...)) for &lt;&gt;.
        // </summary>
        // <returns>
        // A <see cref="SqlBuilder" /> .
        // </returns>
        public override ISqlFragment Visit(DbComparisonExpression e)
        {
            Check.NotNull(e, "e");

            SqlBuilder result;

            // Don't try to optimize the comparison, if one of the sides isn't of type string.
            if (e.Left.ResultType.IsPrimitiveType(PrimitiveTypeKind.String))
            {
                // Check if the Comparison expression is a candidate for compensation in order to optimize store performance.
                _forceNonUnicode = CheckIfForceNonUnicodeRequired(e);
            }

            switch (e.ExpressionKind)
            {
                case DbExpressionKind.Equals:
                    result = VisitComparisonExpression(" = ", e.Left, e.Right);
                    break;
                case DbExpressionKind.LessThan:
                    result = VisitComparisonExpression(" < ", e.Left, e.Right);
                    break;
                case DbExpressionKind.LessThanOrEquals:
                    result = VisitComparisonExpression(" <= ", e.Left, e.Right);
                    break;
                case DbExpressionKind.GreaterThan:
                    result = VisitComparisonExpression(" > ", e.Left, e.Right);
                    break;
                case DbExpressionKind.GreaterThanOrEquals:
                    result = VisitComparisonExpression(" >= ", e.Left, e.Right);
                    break;
                // The parser does not generate the expression kind below.
                case DbExpressionKind.NotEquals:
                    result = VisitComparisonExpression(" <> ", e.Left, e.Right);
                    break;

                default:
                    Debug.Assert(false); // The constructor should have prevented this
                    throw new InvalidOperationException(String.Empty);
            }

            // Reset the force non-unicode, global state variable if it was set by CheckIfForceNonUnicodeRequired().
            _forceNonUnicode = false;

            return result;
        }

        // <summary>
        // Checks if the arguments of the input Comparison or Like expression are candidates
        // for compensation. If yes, sets global state variable - _forceNonUnicode.
        // </summary>
        // <param name="e"> DBComparisonExpression or DbLikeExpression </param>
        private bool CheckIfForceNonUnicodeRequired(DbExpression e)
        {
            if (_forceNonUnicode)
            {
                Debug.Assert(false);
                throw new NotSupportedException();
            }
            return MatchPatternForForcingNonUnicode(e);
        }

        // <summary>
        // The grammar for the pattern that we are looking for is -
        // Pattern := Target OP Source | Source OP Target
        // OP := Like | In | Comparison
        // Source := Non-unicode DbPropertyExpression
        // Target := Target FUNC Target | DbConstantExpression | DBParameterExpression
        // FUNC := CONCAT | RTRIM | LTRIM | TRIM | SUBSTRING | TOLOWER | TOUPPER | REVERSE | REPLACE
        // </summary>
        private bool MatchPatternForForcingNonUnicode(DbExpression e)
        {
            switch (e.ExpressionKind)
            {
                case DbExpressionKind.Like:
                    var likeExpr = (DbLikeExpression)e;
                    return MatchSourcePatternForForcingNonUnicode(likeExpr.Argument) &&
                           MatchTargetPatternForForcingNonUnicode(likeExpr.Pattern) &&
                           MatchTargetPatternForForcingNonUnicode(likeExpr.Escape);

                case DbExpressionKind.In:
                    var inExpr = (DbInExpression)e;
                    return MatchSourcePatternForForcingNonUnicode(inExpr.Item);

                default:
                    // DBExpressionKind is any of (Equals, LessThan, LessThanOrEquals, GreaterThan, GreaterThanOrEquals, NotEquals)
                    var compareExpr = (DbComparisonExpression)e;
                    var left = compareExpr.Left;
                    var right = compareExpr.Right;

                    return (MatchSourcePatternForForcingNonUnicode(left) && MatchTargetPatternForForcingNonUnicode(right)) ||
                           (MatchSourcePatternForForcingNonUnicode(right) && MatchTargetPatternForForcingNonUnicode(left));
            }
        }

        // <summary>
        // Matches the non-terminal symbol "target" in above grammar.
        // </summary>
        internal bool MatchTargetPatternForForcingNonUnicode(DbExpression expr)
        {
            if (IsConstParamOrNullExpressionUnicodeNotSpecified(expr))
            {
                return true;
            }

            if (expr.ExpressionKind
                == DbExpressionKind.Function)
            {
                var functionExpr = (DbFunctionExpression)expr;
                var function = functionExpr.Function;

                if (!function.IsCanonicalFunction()
                    && !SqlFunctionCallHandler.IsStoreFunction(function))
                {
                    return false;
                }

                // All string arguments to the function must be candidates to match target pattern.
                var functionFullName = function.FullName;

                if (_canonicalAndStoreStringFunctionsOneArg.Contains(functionFullName))
                {
                    return MatchTargetPatternForForcingNonUnicode(functionExpr.Arguments[0]);
                }

                if ("Edm.Concat".Equals(functionFullName, StringComparison.Ordinal))
                {
                    return (MatchTargetPatternForForcingNonUnicode(functionExpr.Arguments[0]) &&
                            MatchTargetPatternForForcingNonUnicode(functionExpr.Arguments[1]));
                }

                if ("Edm.Replace".Equals(functionFullName, StringComparison.Ordinal)
                    || "SqlServer.REPLACE".Equals(functionFullName, StringComparison.Ordinal))
                {
                    return (MatchTargetPatternForForcingNonUnicode(functionExpr.Arguments[0]) &&
                            MatchTargetPatternForForcingNonUnicode(functionExpr.Arguments[1]) &&
                            MatchTargetPatternForForcingNonUnicode(functionExpr.Arguments[2]));
                }
            }

            return false;
        }

        // <summary>
        // Determines if the expression represents a non-unicode string column(char/varchar store type)
        // </summary>
        private static bool MatchSourcePatternForForcingNonUnicode(DbExpression argument)
        {
            bool isUnicode;
            return argument.ExpressionKind == DbExpressionKind.Property &&
                   argument.ResultType.TryGetIsUnicode(out isUnicode) &&
                   !isUnicode;
        }

        // <summary>
        // Determines if the expression represents a string constant or parameter with the facet, unicode=null.
        // </summary>
        internal static bool IsConstParamOrNullExpressionUnicodeNotSpecified(DbExpression argument)
        {
            bool isUnicode;
            var expressionKind = argument.ExpressionKind;
            var type = argument.ResultType;

            if (!type.IsPrimitiveType(PrimitiveTypeKind.String))
            {
                return false;
            }

            return (expressionKind == DbExpressionKind.Constant ||
                    expressionKind == DbExpressionKind.ParameterReference ||
                    expressionKind == DbExpressionKind.Null) &&
                   !type.TryGetFacetValue(DbProviderManifest.UnicodeFacetName, out isUnicode);
        }

        // <summary>
        // Generate tsql for a constant. Avoid the explicit cast (if possible) when
        // the isCastOptional parameter is set
        // </summary>
        // <param name="e"> the constant expression </param>
        // <param name="isCastOptional"> can we avoid the CAST </param>
        // <returns> the tsql fragment </returns>
        private ISqlFragment VisitConstant(DbConstantExpression e, bool isCastOptional)
        {
            // Constants will be sent to the store as part of the generated TSQL, not as parameters
            var result = new SqlBuilder();

            var resultType = e.ResultType;
            // Model Types can be (at the time of this implementation):
            //      Binary, Boolean, Byte, Date, DateTime, DateTimeOffset, Decimal, Double, Guid, Int16, Int32, Int64, Single, String, Time
            if (resultType.IsPrimitiveType())
            {
                var typeKind = resultType.GetPrimitiveTypeKind();
                switch (typeKind)
                {
                    case PrimitiveTypeKind.Int32:
                        // default sql server type for integral values.
                        result.Append(e.Value.ToString());
                        break;

                    case PrimitiveTypeKind.Binary:
                        result.Append(" 0x");
                        result.Append(ByteArrayToBinaryString((Byte[])e.Value));
                        result.Append(" ");
                        break;

                    case PrimitiveTypeKind.Boolean:
                        // Bugs 450277, 430294: Need to preserve the boolean type-ness of
                        // this value for round-trippability
                        WrapWithCastIfNeeded(!isCastOptional, (bool)e.Value ? "1" : "0", "bit", result);
                        break;

                    case PrimitiveTypeKind.Byte:
                        WrapWithCastIfNeeded(!isCastOptional, e.Value.ToString(), "tinyint", result);
                        break;

                    case PrimitiveTypeKind.DateTime:
                        result.Append("convert(");
                        result.Append(IsPreKatmai ? "datetime" : "datetime2");
                        result.Append(", ");
                        result.Append(
                            EscapeSingleQuote(
                                ((DateTime)e.Value).ToString(
                                    IsPreKatmai ? "yyyy-MM-dd HH:mm:ss.fff" : "yyyy-MM-dd HH:mm:ss.fffffff", CultureInfo.InvariantCulture),
                                false /* IsUnicode */));
                        result.Append(", 121)");
                        break;

                    case PrimitiveTypeKind.Time:
                        AssertKatmaiOrNewer(typeKind);
                        result.Append("convert(");
                        result.Append(e.ResultType.EdmType.Name);
                        result.Append(", ");
                        result.Append(EscapeSingleQuote(e.Value.ToString(), false /* IsUnicode */));
                        result.Append(", 121)");
                        break;

                    case PrimitiveTypeKind.DateTimeOffset:
                        AssertKatmaiOrNewer(typeKind);
                        result.Append("convert(");
                        result.Append(e.ResultType.EdmType.Name);
                        result.Append(", ");
                        result.Append(
                            EscapeSingleQuote(
                                ((DateTimeOffset)e.Value).ToString("yyyy-MM-dd HH:mm:ss.fffffff zzz", CultureInfo.InvariantCulture), false
                            /* IsUnicode */));
                        result.Append(", 121)");
                        break;

                    case PrimitiveTypeKind.Decimal:
                        var strDecimal = ((Decimal)e.Value).ToString(CultureInfo.InvariantCulture);
                        // if the decimal value has no decimal part, cast as decimal to preserve type
                        // if the number has precision > int64 max precision, it will be handled as decimal by sql server
                        // and does not need cast. if precision is lest then 20, then cast using Max(literal precision, sql default precision)
                        var needsCast = -1 == strDecimal.IndexOf('.') && (strDecimal.TrimStart(new[] { '-' }).Length < 20);

                        var precision = Math.Max((Byte)strDecimal.Length, DefaultDecimalPrecision);
                        Debug.Assert(precision > 0, "Precision must be greater than zero");

                        var decimalType = "decimal(" + precision.ToString(CultureInfo.InvariantCulture) + ")";

                        WrapWithCastIfNeeded(needsCast, strDecimal, decimalType, result);
                        break;

                    case PrimitiveTypeKind.Double:
                        {
                            var doubleValue = (Double)e.Value;
                            AssertValidDouble(doubleValue);
                            WrapWithCastIfNeeded(true, doubleValue.ToString("R", CultureInfo.InvariantCulture), "float(53)", result);
                        }
                        break;

                    case PrimitiveTypeKind.Geography:
                        AppendSpatialConstant(result, ((DbGeography)e.Value).AsSpatialValue());
                        break;

                    case PrimitiveTypeKind.Geometry:
                        AppendSpatialConstant(result, ((DbGeometry)e.Value).AsSpatialValue());
                        break;

                    case PrimitiveTypeKind.Guid:
                        WrapWithCastIfNeeded(true, EscapeSingleQuote(e.Value.ToString(), false /* IsUnicode */), "uniqueidentifier", result);
                        break;

                    case PrimitiveTypeKind.Int16:
                        WrapWithCastIfNeeded(!isCastOptional, e.Value.ToString(), "smallint", result);
                        break;

                    case PrimitiveTypeKind.Int64:
                        WrapWithCastIfNeeded(!isCastOptional, e.Value.ToString(), "bigint", result);
                        break;

                    case PrimitiveTypeKind.Single:
                        {
                            var singleValue = (float)e.Value;
                            AssertValidSingle(singleValue);
                            WrapWithCastIfNeeded(true, singleValue.ToString("R", CultureInfo.InvariantCulture), "real", result);
                        }
                        break;

                    case PrimitiveTypeKind.String:
                        bool isUnicode;

                        if (!e.ResultType.TryGetIsUnicode(out isUnicode))
                        {
                            // If the unicode facet is not specified, if needed force non-unicode, otherwise default to unicode.
                            isUnicode = !_forceNonUnicode;
                        }
                        result.Append(EscapeSingleQuote(e.Value as string, isUnicode));
                        break;

                    default:
                        // all known scalar types should been handled already.
                        throw new NotSupportedException(
                            Strings.NoStoreTypeForEdmType(resultType.EdmType.Name, ((PrimitiveType)(resultType.EdmType)).PrimitiveTypeKind));
                }
            }
            else
            {
                throw new NotSupportedException();
                //if/when Enum types are supported, then handle appropriately, for now is not a valid type for constants.
                //result.Append(e.Value.ToString());
            }

            return result;
        }

        private void AppendSpatialConstant(SqlBuilder result, IDbSpatialValue spatialValue)
        {
            DebugCheck.NotNull(result);
            DebugCheck.NotNull(spatialValue);

            // Spatial constants are represented by calls to a static constructor function. The attempt is made to extract an
            // appropriate representation from the value (which may not implement the required methods). If an SRID value and
            // a text, binary or GML representation of the spatial value can be extracted, the the corresponding function call
            // expression is built and processed.
            DbFunctionExpression functionExpression = null;
            var srid = spatialValue.CoordinateSystemId;
            if (srid.HasValue)
            {
                var wellKnownText = spatialValue.WellKnownText;
                if (wellKnownText != null)
                {
                    functionExpression = (spatialValue.IsGeography
                                              ? SpatialEdmFunctions.GeographyFromText(wellKnownText, srid.Value)
                                              : SpatialEdmFunctions.GeometryFromText(wellKnownText, srid.Value));
                }
                else
                {
                    var wellKnownBinary = spatialValue.WellKnownBinary;
                    if (wellKnownBinary != null)
                    {
                        functionExpression = (spatialValue.IsGeography
                                                  ? SpatialEdmFunctions.GeographyFromBinary(wellKnownBinary, srid.Value)
                                                  : SpatialEdmFunctions.GeometryFromBinary(wellKnownBinary, srid.Value));
                    }
                    else
                    {
                        var gmlString = spatialValue.GmlString;
                        if (gmlString != null)
                        {
                            functionExpression = (spatialValue.IsGeography
                                                      ? SpatialEdmFunctions.GeographyFromGml(gmlString, srid.Value)
                                                      : SpatialEdmFunctions.GeometryFromGml(gmlString, srid.Value));
                        }
                    }
                }
            }

            if (functionExpression != null)
            {
                result.Append(SqlFunctionCallHandler.GenerateFunctionCallSql(this, functionExpression));
            }
            else
            {
                throw spatialValue.NotSqlCompatible();
            }
        }

        // <summary>
        // Helper method for <see cref="VisitConstant" />
        // </summary>
        // <param name="value"> A double value </param>
        // <exception cref="NotSupportedException">
        // If a value of positive or negative infinity, or
        // <see cref="double.NaN" />
        // is specified
        // </exception>
        private static void AssertValidDouble(double value)
        {
            if (double.IsNaN(value))
            {
                throw new NotSupportedException(
                    Strings.SqlGen_TypedNaNNotSupported(Enum.GetName(typeof(PrimitiveTypeKind), PrimitiveTypeKind.Double)));
            }
            else if (double.IsPositiveInfinity(value))
            {
                throw new NotSupportedException(
                    Strings.SqlGen_TypedPositiveInfinityNotSupported(
                        Enum.GetName(typeof(PrimitiveTypeKind), PrimitiveTypeKind.Double), typeof(Double).Name));
            }
            else if (double.IsNegativeInfinity(value))
            {
                throw new NotSupportedException(
                    Strings.SqlGen_TypedNegativeInfinityNotSupported(
                        Enum.GetName(typeof(PrimitiveTypeKind), PrimitiveTypeKind.Double), typeof(Double).Name));
            }
        }

        // <summary>
        // Helper method for <see cref="VisitConstant" />
        // </summary>
        // <param name="value"> A single value </param>
        // <exception cref="NotSupportedException">
        // If a value of positive or negative infinity, or
        // <see cref="float.NaN" />
        // is specified
        // </exception>
        private static void AssertValidSingle(float value)
        {
            if (float.IsNaN(value))
            {
                throw new NotSupportedException(
                    Strings.SqlGen_TypedNaNNotSupported(Enum.GetName(typeof(PrimitiveTypeKind), PrimitiveTypeKind.Single)));
            }
            else if (float.IsPositiveInfinity(value))
            {
                throw new NotSupportedException(
                    Strings.SqlGen_TypedPositiveInfinityNotSupported(
                        Enum.GetName(typeof(PrimitiveTypeKind), PrimitiveTypeKind.Single), typeof(Single).Name));
            }
            else if (float.IsNegativeInfinity(value))
            {
                throw new NotSupportedException(
                    Strings.SqlGen_TypedNegativeInfinityNotSupported(
                        Enum.GetName(typeof(PrimitiveTypeKind), PrimitiveTypeKind.Single), typeof(Single).Name));
            }
        }

        // <summary>
        // Helper function for <see cref="VisitConstant" />
        // Appends the given constant value to the result either 'as is' or wrapped with a cast to the given type.
        // </summary>
        private static void WrapWithCastIfNeeded(bool cast, string value, string typeName, SqlBuilder result)
        {
            if (!cast)
            {
                result.Append(value);
            }
            else
            {
                result.Append("cast(");
                result.Append(value);
                result.Append(" as ");
                result.Append(typeName);
                result.Append(")");
            }
        }

        // <summary>
        // We do not pass constants as parameters.
        // </summary>
        // <returns>
        // A <see cref="SqlBuilder" /> . Strings are wrapped in single quotes and escaped. Numbers are written literally.
        // </returns>
        public override ISqlFragment Visit(DbConstantExpression e)
        {
            Check.NotNull(e, "e");

            return VisitConstant(e, false /* isCastOptional */);
        }

        public override ISqlFragment Visit(DbDerefExpression e)
        {
            Check.NotNull(e, "e");

            throw new NotSupportedException();
        }

        // <summary>
        // The DISTINCT has to be added to the beginning of SqlSelectStatement.Select,
        // but it might be too late for that.  So, we use a flag on SqlSelectStatement
        // instead, and add the "DISTINCT" in the second phase.
        // </summary>
        // <returns>
        // A <see cref="SqlSelectStatement" />
        // </returns>
        public override ISqlFragment Visit(DbDistinctExpression e)
        {
            Check.NotNull(e, "e");

            var result = VisitExpressionEnsureSqlStatement(e.Argument);

            if (!IsCompatible(result, e.ExpressionKind))
            {
                Symbol fromSymbol;
                var inputType = e.Argument.ResultType.GetElementTypeUsage();
                result = CreateNewSelectStatement(result, "distinct", inputType, out fromSymbol);
                AddFromSymbol(result, "distinct", fromSymbol, false);
            }

            result.Select.IsDistinct = true;
            return result;
        }

        // <summary>
        // An element expression returns a scalar - so it is translated to
        // ( Select ... )
        // </summary>
        public override ISqlFragment Visit(DbElementExpression e)
        {
            Check.NotNull(e, "e");

            // ISSUE: What happens if the DbElementExpression is used as an input expression?
            // i.e. adding the '('  might not be right in all cases.
            var result = new SqlBuilder();
            result.Append("(");
            result.Append(VisitExpressionEnsureSqlStatement(e.Argument));
            result.Append(")");

            return result;
        }

        // <summary>
        // <see cref="Visit(DbUnionAllExpression)" />
        // </summary>
        public override ISqlFragment Visit(DbExceptExpression e)
        {
            Check.NotNull(e, "e");

            Debug.Assert(SqlVersion != SqlVersion.Sql8, "DbExceptExpression when translating for SQL Server 2000.");

            return VisitSetOpExpression(e, "EXCEPT");
        }

        // <summary>
        // Only concrete expression types will be visited.
        // </summary>
        public override ISqlFragment Visit(DbExpression e)
        {
            Check.NotNull(e, "e");

            throw new InvalidOperationException(String.Empty);
        }

        // <returns>
        // If we are in a Join context, returns a <see cref="SqlBuilder" /> with the extent name, otherwise, a new
        // <see
        //     cref="SqlSelectStatement" />
        // with the From field set.
        // </returns>
        public override ISqlFragment Visit(DbScanExpression e)
        {
            Check.NotNull(e, "e");

            var target = e.Target;

            // ISSUE: Should we just return a string all the time, and let
            // VisitInputExpression create the SqlSelectStatement?

            var targetTSql = GetTargetTSql(target);

            if (_targets != null)
            {
                _targets.Add(targetTSql);
            }

            if (IsParentAJoin)
            {
                var result = new SqlBuilder();
                result.Append(targetTSql);

                return result;
            }
            else
            {
                var result = new SqlSelectStatement();
                result.From.Append(targetTSql);

                return result;
            }
        }

        // <summary>
        // Gets escaped TSql identifier describing this entity set.
        // </summary>
        internal static string GetTargetTSql(EntitySetBase entitySetBase)
        {
            var definingQuery = entitySetBase.GetMetadataPropertyValue<string>("DefiningQuery");
            if (definingQuery != null)
            {
                return "(" + definingQuery + ")";
            }
            // construct escaped T-SQL referencing entity set
            var builder = new StringBuilder(50);

            var schema = entitySetBase.GetMetadataPropertyValue<string>("Schema");
            if (!string.IsNullOrEmpty(schema))
            {
                builder.Append(QuoteIdentifier(schema));
                builder.Append(".");
            }
            else
            {
                builder.Append(QuoteIdentifier(entitySetBase.EntityContainer.Name));
                builder.Append(".");
            }

            var table = entitySetBase.GetMetadataPropertyValue<string>("Table");
            builder.Append(
                string.IsNullOrEmpty(table)
                    ? QuoteIdentifier(entitySetBase.Name)
                    : QuoteIdentifier(table));

            return builder.ToString();
        }

        // <summary>
        // The bodies of <see cref="Visit(DbFilterExpression)" />, <see cref="Visit(DbGroupByExpression)" />,
        // <see cref="Visit(DbProjectExpression)" />, <see cref="Visit(DbSortExpression)" /> are similar.
        // Each does the following.
        // <list type="number">
        //     <item>Visit the input expression</item>
        //     <item>
        //         Determine if the input's SQL statement can be reused, or a new
        //         one must be created.
        //     </item>
        //     <item>Create a new symbol table scope</item>
        //     <item>
        //         Push the Sql statement onto a stack, so that children can
        //         update the free variable list.
        //     </item>
        //     <item>Visit the non-input expression.</item>
        //     <item>Cleanup</item>
        // </list>
        // </summary>
        // <returns>
        // A <see cref="SqlSelectStatement" />
        // </returns>
        public override ISqlFragment Visit(DbFilterExpression e)
        {
            Check.NotNull(e, "e");

            return VisitFilterExpression(e.Input, e.Predicate, false);
        }

        // <summary>
        // Lambda functions are not supported.
        // The functions supported are:
        // <list type="number">
        //     <item>Canonical Functions - We recognize these by their dataspace, it is DataSpace.CSpace</item>
        //     <item>Store Functions - We recognize these by the BuiltInAttribute and not being Canonical</item>
        //     <item>User-defined Functions - All the rest</item>
        // </list>
        // We handle Canonical and Store functions the same way: If they are in the list of functions
        // that need special handling, we invoke the appropriate handler, otherwise we translate them to
        // FunctionName(arg1, arg2, ..., argn).
        // We translate user-defined functions to NamespaceName.FunctionName(arg1, arg2, ..., argn).
        // </summary>
        // <returns>
        // A <see cref="SqlBuilder" />
        // </returns>
        public override ISqlFragment Visit(DbFunctionExpression e)
        {
            Check.NotNull(e, "e");

            return SqlFunctionCallHandler.GenerateFunctionCallSql(this, e);
        }

        public override ISqlFragment Visit(DbLambdaExpression expression)
        {
            Check.NotNull(expression, "expression");

            throw new NotSupportedException();
        }

        public override ISqlFragment Visit(DbEntityRefExpression e)
        {
            Check.NotNull(e, "e");

            throw new NotSupportedException();
        }

        public override ISqlFragment Visit(DbRefKeyExpression e)
        {
            Check.NotNull(e, "e");

            throw new NotSupportedException();
        }

        // <summary>
        // <see cref="Visit(DbFilterExpression)" /> for general details.
        // We modify both the GroupBy and the Select fields of the SqlSelectStatement.
        // GroupBy gets just the keys without aliases,
        // and Select gets the keys and the aggregates with aliases.
        // Sql Server does not support arbitrarily complex expressions inside aggregates,
        // and requires keys to have reference to the input scope,
        // so in some cases we create a nested query in which we alias the arguments to the aggregates.
        // The exact limitations of Sql Server are:
        // <list type="number">
        //     <item>
        //         If an expression being aggregated contains an outer reference, then that outer
        //         reference must be the only column referenced in the expression (SQLBUDT #488741)
        //     </item>
        //     <item>
        //         Sql Server cannot perform an aggregate function on an expression containing
        //         an aggregate or a subquery. (SQLBUDT #504600)
        //     </item>
        //     <item>
        //         Sql Server requries each GROUP BY expression (key) to contain at least one column
        //         that is not an outer reference. (SQLBUDT #616523)
        //     </item>
        //     <item>
        //         Aggregates on the right side of an APPLY cannot reference columns from the left side.
        //         (SQLBUDT #617683)
        //     </item>
        // </list>
        // The default translation, without inner query is:
        // SELECT
        // kexp1 AS key1, kexp2 AS key2,... kexpn AS keyn,
        // aggf1(aexpr1) AS agg1, .. aggfn(aexprn) AS aggn
        // FROM input AS a
        // GROUP BY kexp1, kexp2, .. kexpn
        // When we inject an innner query, the equivalent translation is:
        // SELECT
        // key1 AS key1, key2 AS key2, .. keyn AS keys,
        // aggf1(agg1) AS agg1, aggfn(aggn) AS aggn
        // FROM (
        // SELECT
        // kexp1 AS key1, kexp2 AS key2,... kexpn AS keyn,
        // aexpr1 AS agg1, .. aexprn AS aggn
        // FROM input AS a
        // ) as a
        // GROUP BY key1, key2, keyn
        // </summary>
        // <returns>
        // A <see cref="SqlSelectStatement" />
        // </returns>
        public override ISqlFragment Visit(DbGroupByExpression e)
        {
            Check.NotNull(e, "e");

            Symbol fromSymbol;
            var innerQuery = VisitInputExpression(
                e.Input.Expression,
                e.Input.VariableName, e.Input.VariableType, out fromSymbol);

            // GroupBy is compatible with Filter and OrderBy
            // but not with Project, GroupBy
            if (!IsCompatible(innerQuery, e.ExpressionKind))
            {
                innerQuery = CreateNewSelectStatement(innerQuery, e.Input.VariableName, e.Input.VariableType, out fromSymbol);
            }

            selectStatementStack.Push(innerQuery);
            symbolTable.EnterScope();

            AddFromSymbol(innerQuery, e.Input.VariableName, fromSymbol);
            // This line is not present for other relational nodes.
            symbolTable.Add(e.Input.GroupVariableName, fromSymbol);

            // The enumerator is shared by both the keys and the aggregates,
            // so, we do not close it in between.
            var groupByType = (RowType)((CollectionType)e.ResultType.EdmType).TypeUsage.EdmType;

            //SQL Server does not support arbitrarily complex expressions inside aggregates, 
            // and requires keys to have reference to the input scope, 
            // so we check for the specific restrictions and if need we inject an inner query.
            var needsInnerQuery = GroupByAggregatesNeedInnerQuery(e.Aggregates, e.Input.GroupVariableName)
                                  || GroupByKeysNeedInnerQuery(e.Keys, e.Input.VariableName);

            SqlSelectStatement result;
            if (needsInnerQuery)
            {
                //Create the inner query
                result = CreateNewSelectStatement(innerQuery, e.Input.VariableName, e.Input.VariableType, false, out fromSymbol);
                AddFromSymbol(result, e.Input.VariableName, fromSymbol, false);
            }
            else
            {
                result = innerQuery;
            }

            using (IEnumerator<EdmProperty> members = groupByType.Properties.GetEnumerator())
            {
                members.MoveNext();
                Debug.Assert(result.Select.IsEmpty);

                var separator = "";

                foreach (var key in e.Keys)
                {
                    var member = members.Current;
                    var alias = QuoteIdentifier(member.Name);

                    result.GroupBy.Append(separator);

                    var keySql = key.Accept(this);

                    if (!needsInnerQuery)
                    {
                        //Default translation: Key AS Alias
                        result.Select.Append(separator);
                        result.Select.AppendLine();
                        result.Select.Append(keySql);
                        result.Select.Append(" AS ");
                        result.Select.Append(alias);

                        result.GroupBy.Append(keySql);
                    }
                    else
                    {
                        // The inner query contains the default translation Key AS Alias
                        innerQuery.Select.Append(separator);
                        innerQuery.Select.AppendLine();
                        innerQuery.Select.Append(keySql);
                        innerQuery.Select.Append(" AS ");
                        innerQuery.Select.Append(alias);

                        //The outer resulting query projects over the key aliased in the inner query: 
                        //  fromSymbol.Alias AS Alias
                        result.Select.Append(separator);
                        result.Select.AppendLine();
                        result.Select.Append(fromSymbol);
                        result.Select.Append(".");
                        result.Select.Append(alias);
                        result.Select.Append(" AS ");
                        result.Select.Append(alias);

                        result.GroupBy.Append(alias);
                    }

                    separator = ", ";
                    members.MoveNext();
                }

                foreach (var aggregate in e.Aggregates)
                {
                    var member = members.Current;
                    var alias = QuoteIdentifier(member.Name);

                    Debug.Assert(aggregate.Arguments.Count == 1);
                    var translatedAggregateArgument = aggregate.Arguments[0].Accept(this);

                    object aggregateArgument;

                    if (needsInnerQuery)
                    {
                        //In this case the argument to the aggratete is reference to the one projected out by the
                        // inner query
                        var wrappingAggregateArgument = new SqlBuilder();
                        wrappingAggregateArgument.Append(fromSymbol);
                        wrappingAggregateArgument.Append(".");
                        wrappingAggregateArgument.Append(alias);
                        aggregateArgument = wrappingAggregateArgument;

                        innerQuery.Select.Append(separator);
                        innerQuery.Select.AppendLine();
                        innerQuery.Select.Append(translatedAggregateArgument);
                        innerQuery.Select.Append(" AS ");
                        innerQuery.Select.Append(alias);
                    }
                    else
                    {
                        aggregateArgument = translatedAggregateArgument;
                    }

                    ISqlFragment aggregateResult = VisitAggregate(aggregate, aggregateArgument);

                    result.Select.Append(separator);
                    result.Select.AppendLine();
                    result.Select.Append(aggregateResult);
                    result.Select.Append(" AS ");
                    result.Select.Append(alias);

                    separator = ", ";
                    members.MoveNext();
                }
            }

            symbolTable.ExitScope();
            selectStatementStack.Pop();

            return result;
        }

        // <summary>
        // <see cref="Visit(DbUnionAllExpression)" />
        // </summary>
        public override ISqlFragment Visit(DbIntersectExpression e)
        {
            Check.NotNull(e, "e");

            Debug.Assert(SqlVersion != SqlVersion.Sql8, "DbIntersectExpression when translating for SQL Server 2000.");

            return VisitSetOpExpression(e, "INTERSECT");
        }

        // <summary>
        // Not(IsEmpty) has to be handled specially, so we delegate to
        // <see cref="VisitIsEmptyExpression" />.
        // </summary>
        // <returns>
        // A <see cref="SqlBuilder" /> . <code>[NOT] EXISTS( ... )</code>
        // </returns>
        public override ISqlFragment Visit(DbIsEmptyExpression e)
        {
            Check.NotNull(e, "e");

            return VisitIsEmptyExpression(e, false);
        }

        // <summary>
        // Not(IsNull) is handled specially, so we delegate to
        // <see cref="VisitIsNullExpression" />
        // </summary>
        // <returns>
        // A <see cref="SqlBuilder" /> <code>IS [NOT] NULL</code>
        // </returns>
        public override ISqlFragment Visit(DbIsNullExpression e)
        {
            Check.NotNull(e, "e");

            return VisitIsNullExpression(e, false);
        }

        // <summary>
        // No error is raised if the store cannot support this.
        // </summary>
        // <returns>
        // A <see cref="SqlBuilder" />
        // </returns>
        public override ISqlFragment Visit(DbIsOfExpression e)
        {
            Check.NotNull(e, "e");

            throw new NotSupportedException();
        }

        // <summary>
        // <see cref="VisitJoinExpression" />
        // </summary>
        // <returns>
        // A <see cref="SqlSelectStatement" /> .
        // </returns>
        public override ISqlFragment Visit(DbCrossJoinExpression e)
        {
            Check.NotNull(e, "e");

            return VisitJoinExpression(e.Inputs, e.ExpressionKind, "CROSS JOIN", null);
        }

        // <summary>
        // <see cref="VisitJoinExpression" />
        // </summary>
        // <returns>
        // A <see cref="SqlSelectStatement" /> .
        // </returns>
        public override ISqlFragment Visit(DbJoinExpression e)
        {
            Check.NotNull(e, "e");

            #region Map join type to a string

            string joinString;
            switch (e.ExpressionKind)
            {
                case DbExpressionKind.FullOuterJoin:
                    joinString = "FULL OUTER JOIN";
                    break;

                case DbExpressionKind.InnerJoin:
                    joinString = "INNER JOIN";
                    break;

                case DbExpressionKind.LeftOuterJoin:
                    joinString = "LEFT OUTER JOIN";
                    break;

                default:
                    Debug.Assert(false);
                    joinString = null;
                    break;
            }

            #endregion

            var inputs = new List<DbExpressionBinding>(2);
            inputs.Add(e.Left);
            inputs.Add(e.Right);

            return VisitJoinExpression(inputs, e.ExpressionKind, joinString, e.JoinCondition);
        }

        // <returns>
        // A <see cref="SqlBuilder" />
        // </returns>
        public override ISqlFragment Visit(DbLikeExpression e)
        {
            Check.NotNull(e, "e");

            // Check if the LIKE expression is a candidate for compensation in order to optimize store performance.
            _forceNonUnicode = CheckIfForceNonUnicodeRequired(e);

            var result = new SqlBuilder();
            result.Append(e.Argument.Accept(this));
            result.Append(" LIKE ");
            result.Append(e.Pattern.Accept(this));

            // if the ESCAPE expression is a DbNullExpression, then that's tantamount to 
            // not having an ESCAPE at all
            if (e.Escape.ExpressionKind
                != DbExpressionKind.Null)
            {
                result.Append(" ESCAPE ");
                result.Append(e.Escape.Accept(this));
            }

            // Reset the force non-unicode, global state variable if it was set by CheckIfForceNonUnicodeRequired().
            _forceNonUnicode = false;

            return result;
        }

        // <summary>
        // Translates to TOP expression. For Sql8, limit can only be a constant expression
        // </summary>
        // <returns>
        // A <see cref="SqlBuilder" />
        // </returns>
        public override ISqlFragment Visit(DbLimitExpression e)
        {
            Check.NotNull(e, "e");

            Debug.Assert(
                e.Limit is DbConstantExpression || e.Limit is DbParameterReferenceExpression,
                "DbLimitExpression.Limit is of invalid expression type");
            Debug.Assert(
                !((SqlVersion == SqlVersion.Sql8) && (e.Limit is DbParameterReferenceExpression)),
                "DbLimitExpression.Limit is DbParameterReferenceExpression for SQL Server 2000.");

            var result = VisitExpressionEnsureSqlStatement(e.Argument, false, false);

            if (!IsCompatible(result, e.ExpressionKind))
            {
                var inputType = e.Argument.ResultType.GetElementTypeUsage();

                Symbol fromSymbol;
                result = CreateNewSelectStatement(result, "top", inputType, out fromSymbol);
                AddFromSymbol(result, "top", fromSymbol, false);
            }

            var topCount = HandleCountExpression(e.Limit);

            result.Select.Top = new TopClause(topCount, e.WithTies);
            return result;
        }

        // <summary>
        // DbNewInstanceExpression is allowed as a child of DbProjectExpression only.
        // If anyone else is the parent, we throw.
        // We also perform special casing for collections - where we could convert
        // them into Unions
        // <see cref="VisitNewInstanceExpression" /> for the actual implementation.
        // </summary>
        public override ISqlFragment Visit(DbNewInstanceExpression e)
        {
            Check.NotNull(e, "e");

            if (BuiltInTypeKind.CollectionType
                == e.ResultType.EdmType.BuiltInTypeKind)
            {
                return VisitCollectionConstructor(e);
            }
            throw new NotSupportedException();
        }

        // <summary>
        // The Not expression may cause the translation of its child to change.
        // These children are
        // <list type="bullet">
        //     <item>
        //         <see cref="DbNotExpression" />
        //         NOT(Not(x)) becomes x
        //     </item>
        //     <item>
        //         <see cref="DbIsEmptyExpression" />
        //         NOT EXISTS becomes EXISTS
        //     </item>
        //     <item>
        //         <see cref="DbIsNullExpression" />
        //         IS NULL becomes IS NOT NULL
        //     </item>
        //     <item>
        //         <see cref="DbComparisonExpression" />
        //         = becomes &lt;&gt;
        //     </item>
        // </list>
        // </summary>
        // <returns>
        // A <see cref="SqlBuilder" />
        // </returns>
        public override ISqlFragment Visit(DbNotExpression e)
        {
            Check.NotNull(e, "e");

            // Flatten Not(Not(x)) to x.
            var notExpression = e.Argument as DbNotExpression;
            if (notExpression != null)
            {
                return notExpression.Argument.Accept(this);
            }

            var isEmptyExpression = e.Argument as DbIsEmptyExpression;
            if (isEmptyExpression != null)
            {
                return VisitIsEmptyExpression(isEmptyExpression, true);
            }

            var isNullExpression = e.Argument as DbIsNullExpression;
            if (isNullExpression != null)
            {
                return VisitIsNullExpression(isNullExpression, true);
            }

            var comparisonExpression = e.Argument as DbComparisonExpression;
            if (comparisonExpression != null)
            {
                if (comparisonExpression.ExpressionKind == DbExpressionKind.Equals)
                {
                    var forceNonUnicodeLocal = _forceNonUnicode; // Save flag
                    // Don't try to optimize the comparison, if one of the sides isn't of type string.
                    if (comparisonExpression.Left.ResultType.IsPrimitiveType(PrimitiveTypeKind.String))
                    {
                        _forceNonUnicode = CheckIfForceNonUnicodeRequired(comparisonExpression);
                    }

                    var binaryResult = VisitComparisonExpression(" <> ", comparisonExpression.Left, comparisonExpression.Right);
                    
                    _forceNonUnicode = forceNonUnicodeLocal; // Reset flag
                    return binaryResult;
                }
            }

            var result = new SqlBuilder();
            result.Append(" NOT (");
            result.Append(e.Argument.Accept(this));
            result.Append(")");

            return result;
        }

        // <returns>
        // <see cref="SqlBuilder" />
        // </returns>
        public override ISqlFragment Visit(DbNullExpression e)
        {
            Check.NotNull(e, "e");

            var result = new SqlBuilder();

            // always cast nulls - sqlserver doesn't like case expressions where the "then" clause is null
            result.Append("CAST(NULL AS ");
            var type = e.ResultType;

            //
            // Use the narrowest type possible - especially for strings where we don't want 
            // to produce unicode strings always.
            //
            Debug.Assert(BuiltInTypeKind.PrimitiveType == type.EdmType.BuiltInTypeKind, "Type must be primitive type");
            var primitiveType = type.EdmType as PrimitiveType;
            switch (primitiveType.PrimitiveTypeKind)
            {
                case PrimitiveTypeKind.String:
                    result.Append("varchar(1)");
                    break;
                case PrimitiveTypeKind.Binary:
                    result.Append("varbinary(1)");
                    break;
                default:
                    result.Append(GetSqlPrimitiveType(type));
                    break;
            }

            result.Append(")");
            return result;
        }

        // <returns>
        // A <see cref="SqlBuilder" />
        // </returns>
        public override ISqlFragment Visit(DbOfTypeExpression e)
        {
            Check.NotNull(e, "e");

            throw new NotSupportedException();
        }

        // <summary>
        // Visit a DbOrExpression and consider the subexpressions
        // for whether to generate OR conditions or an IN clause.
        // </summary>
        // <param name="e"> DbOrExpression to be visited </param>
        // <returns>
        // A <see cref="SqlBuilder" /> fragment of SQL generated
        // </returns>
        // <seealso cref="Visit(DbAndExpression)" />
        public override ISqlFragment Visit(DbOrExpression e)
        {
            Check.NotNull(e, "e");

            ISqlFragment result = null;
            if (TryTranslateIntoIn(e, out result))
            {
                return result;
            }

            return VisitBinaryExpression(" OR ", e.ExpressionKind, e.Left, e.Right);
        }

        // <summary>
        // Visits a DbInExpression and generates the corresponding SQL fragment.
        // </summary>
        // <param name="e">
        // A <see cref="DbInExpression" /> that specifies the expression to be visited.
        // </param>
        // <returns>
        // A <see cref="SqlBuilder" /> that specifies the generated SQL fragment.
        // </returns>
        public override ISqlFragment Visit(DbInExpression e)
        {
            Check.NotNull(e, "e");

            if (e.List.Count == 0)
            {
                return Visit(DbExpressionBuilder.False);
            }

            var result = new SqlBuilder();

            // Do not optimize the comparison, if the item to be matched is not of type string.
            if (e.Item.ResultType.IsPrimitiveType(PrimitiveTypeKind.String))
            {
                // Check if the expression is a candidate for compensation in order to optimize store performance.
                _forceNonUnicode = CheckIfForceNonUnicodeRequired(e);
            }

            result.Append(e.Item.Accept(this));
            result.Append(" IN (");

            var first = true;
            foreach (var item in e.List)
            {
                if (first)
                {
                    first = false;
                }
                else
                {
                    result.Append(", ");
                }

                result.Append(item.Accept(this));
            }

            result.Append(")");

            _forceNonUnicode = false;

            return result;
        }

        internal static IDictionary<DbExpression, IList<DbExpression>> HasBuiltMapForIn(DbOrExpression expression)
        {
            var map = new Dictionary<DbExpression, IList<DbExpression>>(new KeyFieldExpressionComparer());

            // Note that map may not be empty even if HasBuiltMapForIn below returns false, but if
            // it does return true then map is known to be not empty.
            return HasBuiltMapForIn(expression, map) ? map : null;
        }

        // <summary>
        // Determine if a DbOrExpression can be optimized into one or more IN clauses
        // and generate an ISqlFragment if it is possible.
        // </summary>
        // <param name="e"> DbOrExpression to attempt translation upon </param>
        // <param name="sqlFragment"> Fragment of SQL generated </param>
        // <returns> True if an IN clause is possible and sqlFragment has been generated, false otherwise </returns>
        private bool TryTranslateIntoIn(DbOrExpression e, out ISqlFragment sqlFragment)
        {
            var map = HasBuiltMapForIn(e);
            if (map == null)
            {
                sqlFragment = null;
                return false;
            }

            var sqlBuilder = new SqlBuilder();
            var firstKey = true;
            foreach (var key in map.Keys)
            {
                var values = map[key];
                if (!firstKey)
                {
                    sqlBuilder.Append(" OR ");
                }
                else
                {
                    firstKey = false;
                }

                var realValues = values.Where(v => v.ExpressionKind != DbExpressionKind.IsNull);
                var realValueCount = realValues.Count();

                // 
                // Should non-unicode be forced over the key or any of the values
                // If the key qualifies as a source, we force it over the values that qualify as targets
                // If all the values qualify as sources, we force it over the key
                //
                var forceNonUnicodeOnQualifyingValues = false;
                var forceNonUnicodeOnKey = false;
                if (key.ResultType.IsPrimitiveType(PrimitiveTypeKind.String))
                {
                    forceNonUnicodeOnQualifyingValues = MatchSourcePatternForForcingNonUnicode(key);
                    forceNonUnicodeOnKey = !forceNonUnicodeOnQualifyingValues && MatchTargetPatternForForcingNonUnicode(key)
                                           && realValues.All(MatchSourcePatternForForcingNonUnicode);
                }

                if (realValueCount == 1)
                {
                    // When only one value we leave it as an equality test
                    HandleInKey(sqlBuilder, key, forceNonUnicodeOnKey);
                    sqlBuilder.Append(" = ");
                    var value = realValues.First();

                    HandleInValue(sqlBuilder, value, key.ResultType.EdmType == value.ResultType.EdmType, forceNonUnicodeOnQualifyingValues);
                }

                if (realValueCount > 1)
                {
                    // More than one value becomes an IN
                    HandleInKey(sqlBuilder, key, forceNonUnicodeOnKey);
                    sqlBuilder.Append(" IN (");

                    var firstValue = true;
                    foreach (var value in realValues)
                    {
                        if (!firstValue)
                        {
                            sqlBuilder.Append(",");
                        }
                        else
                        {
                            firstValue = false;
                        }
                        HandleInValue(
                            sqlBuilder, value, key.ResultType.EdmType == value.ResultType.EdmType, forceNonUnicodeOnQualifyingValues);
                    }
                    sqlBuilder.Append(")");
                }

                // Deal with a null for this key
                var isNullExpression = values.FirstOrDefault(v => v.ExpressionKind == DbExpressionKind.IsNull) as DbIsNullExpression;
                if (isNullExpression != null)
                {
                    if (realValueCount > 0)
                    {
                        sqlBuilder.Append(" OR ");
                    }
                    sqlBuilder.Append(VisitIsNullExpression(isNullExpression, false)); // We never try to build IN with a NOT in the tree
                }
            }

            sqlFragment = sqlBuilder;
            return true;
        }

        private void HandleInValue(SqlBuilder sqlBuilder, DbExpression value, bool isSameEdmType, bool forceNonUnicodeOnQualifyingValues)
        {
            ForcingNonUnicode(
                () => ParenthesizeExpressionWithoutRedundantConstantCasts(value, sqlBuilder, isSameEdmType),
                forceNonUnicodeOnQualifyingValues && MatchTargetPatternForForcingNonUnicode(value));
        }

        private void HandleInKey(SqlBuilder sqlBuilder, DbExpression key, bool forceNonUnicodeOnKey)
        {
            ForcingNonUnicode(() => ParenthesizeExpressionIfNeeded(key, sqlBuilder), forceNonUnicodeOnKey);
        }

        private void ForcingNonUnicode(Action action, bool forceNonUnicode)
        {
            var reset = false;
            if (forceNonUnicode && !_forceNonUnicode)
            {
                _forceNonUnicode = true;
                reset = true;
            }
            action();
            if (reset)
            {
                _forceNonUnicode = false;
            }
        }

        private void ParenthesizeExpressionWithoutRedundantConstantCasts(DbExpression value, SqlBuilder sqlBuilder, Boolean isSameEdmType)
        {
            switch (value.ExpressionKind)
            {
                case DbExpressionKind.Constant:
                    {
                        // We don't want unnecessary casts
                        sqlBuilder.Append(VisitConstant((DbConstantExpression)value, isSameEdmType));
                        break;
                    }
                default:
                    {
                        ParenthesizeExpressionIfNeeded(value, sqlBuilder);
                        break;
                    }
            }
        }

        // <summary>
        // Required by the KeyToListMap to allow certain DbExpression subclasses to be used as a key
        // which is not normally possible given their lack of Equals and GetHashCode implementations
        // for testing object value equality.
        // </summary>
        internal class KeyFieldExpressionComparer : IEqualityComparer<DbExpression>
        {
            // <summary>
            // Compare two DbExpressions to see if they are equal for the purposes of
            // our key management. We only support DbPropertyExpression, DbParameterReferenceExpression,
            // VariableReferenceExpression and DbCastExpression types. Everything else will fail to
            // be considered equal.
            // </summary>
            // <param name="x"> First DbExpression to consider for equality </param>
            // <param name="y"> Second DbExpression to consider for equality </param>
            // <returns> True if the types are allowed and equal, false otherwise </returns>
            public bool Equals(DbExpression x, DbExpression y)
            {
                if (x.ExpressionKind
                    != y.ExpressionKind)
                {
                    return false;
                }

                switch (x.ExpressionKind)
                {
                    case DbExpressionKind.Property:
                        {
                            var first = (DbPropertyExpression)x;
                            var second = (DbPropertyExpression)y;
                            return first.Property == second.Property && Equals(first.Instance, second.Instance);
                        }
                    case DbExpressionKind.ParameterReference:
                        return ((DbParameterReferenceExpression)x).ParameterName == ((DbParameterReferenceExpression)y).ParameterName;

                    case DbExpressionKind.VariableReference:
                        return ReferenceEquals(x, y);

                    case DbExpressionKind.Cast:
                        {
                            var first = (DbCastExpression)x;
                            var second = (DbCastExpression)y;
                            return first.ResultType == second.ResultType && Equals(first.Argument, second.Argument);
                        }
                }

                return false;
            }

            // <summary>
            // Calculates a hashcode for a given number of DbExpression subclasses to allow the KeyToListMap
            // to efficiently and reliably locate existing keys.
            // </summary>
            // <param name="obj"> DbExpression to calculate a hashcode for </param>
            // <returns> Integer containing the hashcode </returns>
            public int GetHashCode(DbExpression obj)
            {
                switch (obj.ExpressionKind)
                {
                    case DbExpressionKind.Property:
                        return ((DbPropertyExpression)obj).Property.GetHashCode();

                    case DbExpressionKind.ParameterReference:
                        return ((DbParameterReferenceExpression)obj).ParameterName.GetHashCode() ^ Int32.MaxValue;

                    case DbExpressionKind.VariableReference:
                        return ((DbVariableReferenceExpression)obj).VariableName.GetHashCode();

                    case DbExpressionKind.Cast:
                        return GetHashCode(((DbCastExpression)obj).Argument);

                    default:
                        return obj.GetHashCode();
                }
            }
        }

        // <summary>
        // Determines if a DbExpression is a valid key for the purposes of generating an In clause optimization.
        // </summary>
        // <param name="e"> DbExpression to consider </param>
        // <returns> True if the expression can be used as a key, false otherwise </returns>
        internal static bool IsKeyForIn(DbExpression e)
        {
            return (e.ExpressionKind == DbExpressionKind.Property
                    || e.ExpressionKind == DbExpressionKind.VariableReference
                    || e.ExpressionKind == DbExpressionKind.ParameterReference);
        }

        // <summary>
        // Looks at both sides of a DbBinaryExpression to consider if either side is a valid candidate to
        // be a key and if so adds it to the KeyToListMap as a key with the other side as the value.
        // </summary>
        // <param name="e"> DbBinaryExpression to consider </param>
        // <param name="values"> KeyToListMap to add the sides of the binary expression to </param>
        // <returns> True if the expression was added, false otherwise </returns>
        internal static bool TryAddExpressionForIn(DbBinaryExpression e, IDictionary<DbExpression, IList<DbExpression>> values)
        {
            if (IsKeyForIn(e.Left))
            {
                values.Add(e.Left, e.Right);
                return true;
            }

            if (IsKeyForIn(e.Right))
            {
                values.Add(e.Right, e.Left);
                return true;
            }

            return false;
        }

        // <summary>
        // Attempts to build a KeyToListMap containing valid references and the appropriate value equality
        // tests associated with each so that they can be optimized into IN clauses. Calls itself recursively
        // to consider additional OR branches.
        // </summary>
        // <param name="e"> DbExpression representing the branch to evaluate </param>
        // <param name="values"> KeyToListMap to which to add references and value equality tests encountered </param>
        // <returns> True if this branch contained just equality tests or further OR branches, false otherwise </returns>
        [SuppressMessage("Microsoft.Performance", "CA1800:DoNotCastUnnecessarily")]
        internal static bool HasBuiltMapForIn(DbExpression e, IDictionary<DbExpression, IList<DbExpression>> values)
        {
            switch (e.ExpressionKind)
            {
                case DbExpressionKind.Equals:
                    return TryAddExpressionForIn((DbBinaryExpression)e, values);

                case DbExpressionKind.IsNull:
                    {
                        var potentialKey = ((DbIsNullExpression)e).Argument;
                        if (IsKeyForIn(potentialKey))
                        {
                            values.Add(potentialKey, e);
                            return true;
                        }
                        return false;
                    }
                case DbExpressionKind.Or:
                    {
                        var comparisonExpression = (DbBinaryExpression)e;
                        return HasBuiltMapForIn(comparisonExpression.Left, values) && HasBuiltMapForIn(comparisonExpression.Right, values);
                    }
                default:
                    return false;
            }
        }

        // <summary>
        // This method handles the DBParameterReference expressions. If the parameter is in
        // a part of the tree, which matches our criteria for forcing to non-unicode, then
        // we add it to the list of candidate parameters. If the parameter occurs in a different
        // usage scenario, then disqualify it from being forced to non-unicode.
        // </summary>
        // <returns>
        // A <see cref="SqlBuilder" />
        // </returns>
        public override ISqlFragment Visit(DbParameterReferenceExpression e)
        {
            Check.NotNull(e, "e");

            // Update the dictionary value only if we are not inside a DbIsNullExpression.
            if (!_ignoreForceNonUnicodeFlag)
            {
                if (!_forceNonUnicode)
                {
                    //This parameter is being used in a different way than in the force non-unicode pattern. So disqualify it.
                    _candidateParametersToForceNonUnicode[e.ParameterName] = false;
                }
                else if (!_candidateParametersToForceNonUnicode.ContainsKey(e.ParameterName))
                {
                    //This parameter matches our criteria for forcing to non-unicode. So add to dictionary
                    _candidateParametersToForceNonUnicode[e.ParameterName] = true;
                }
            }

            var result = new SqlBuilder();

            // Do not quote this name.
            // ISSUE: We are not checking that e.Name has no illegal characters. e.g. space
            result.Append("@" + e.ParameterName);

            return result;
        }

        // <summary>
        // <see cref="Visit(DbFilterExpression)" /> for the general ideas.
        // </summary>
        // <returns>
        // A <see cref="SqlSelectStatement" />
        // </returns>
        // <seealso cref="Visit(DbFilterExpression)" />
        public override ISqlFragment Visit(DbProjectExpression e)
        {
            Check.NotNull(e, "e");

            Symbol fromSymbol;
            var result = VisitInputExpression(e.Input.Expression, e.Input.VariableName, e.Input.VariableType, out fromSymbol);

            //#444002 Aliases need renaming only for Sql8 when there is Order By 
            var aliasesNeedRenaming = false;

            // Project is compatible with Filter
            // but not with Project, GroupBy
            if (!IsCompatible(result, e.ExpressionKind))
            {
                result = CreateNewSelectStatement(result, e.Input.VariableName, e.Input.VariableType, out fromSymbol);
            }
            else if ((SqlVersion == SqlVersion.Sql8)
                     && !result.OrderBy.IsEmpty)
            {
                aliasesNeedRenaming = true;
            }

            selectStatementStack.Push(result);
            symbolTable.EnterScope();

            AddFromSymbol(result, e.Input.VariableName, fromSymbol);

            // Project is the only node that can have DbNewInstanceExpression as a child
            // so we have to check it here.
            // We call VisitNewInstanceExpression instead of Visit(DbNewInstanceExpression), since
            // the latter throws.
            var newInstanceExpression = e.Projection as DbNewInstanceExpression;
            if (newInstanceExpression != null)
            {
                Dictionary<string, Symbol> newColumns;
                result.Select.Append(VisitNewInstanceExpression(newInstanceExpression, aliasesNeedRenaming, out newColumns));
                if (aliasesNeedRenaming)
                {
                    result.OutputColumnsRenamed = true;
                }
                result.OutputColumns = newColumns;
            }
            else
            {
                result.Select.Append(e.Projection.Accept(this));
            }

            symbolTable.ExitScope();
            selectStatementStack.Pop();

            return result;
        }

        // <summary>
        // This method handles record flattening, which works as follows.
        // consider an expression <c>Prop(y, Prop(x, Prop(d, Prop(c, Prop(b, Var(a)))))</c>
        // where a,b,c are joins, d is an extent and x and y are fields.
        // b has been flattened into a, and has its own SELECT statement.
        // c has been flattened into b.
        // d has been flattened into c.
        // We visit the instance, so we reach Var(a) first.  This gives us a (join)symbol.
        // Symbol(a).b gives us a join symbol, with a SELECT statement i.e. Symbol(b).
        // From this point on , we need to remember Symbol(b) as the source alias,
        // and then try to find the column.  So, we use a SymbolPair.
        // We have reached the end when the symbol no longer points to a join symbol.
        // </summary>
        // <returns>
        // A <see cref="JoinSymbol" /> if we have not reached the first Join node that has a SELECT statement. A
        // <see
        //     cref="SymbolPair" />
        // if we have seen the JoinNode, and it has a SELECT statement. A <see cref="SqlBuilder" /> with {Input}.propertyName otherwise.
        // </returns>
        public override ISqlFragment Visit(DbPropertyExpression e)
        {
            Check.NotNull(e, "e");

            SqlBuilder result;

            var instanceSql = e.Instance.Accept(this);

            // Since the DbVariableReferenceExpression is a proper child of ours, we can reset
            // isVarSingle.
            var VariableReferenceExpression = e.Instance as DbVariableReferenceExpression;
            if (VariableReferenceExpression != null)
            {
                isVarRefSingle = false;
            }

            // We need to flatten, and have not yet seen the first nested SELECT statement.
            var joinSymbol = instanceSql as JoinSymbol;
            if (joinSymbol != null)
            {
                Debug.Assert(joinSymbol.NameToExtent.ContainsKey(e.Property.Name));
                if (joinSymbol.IsNestedJoin)
                {
                    return new SymbolPair(joinSymbol, joinSymbol.NameToExtent[e.Property.Name]);
                }
                else
                {
                    return joinSymbol.NameToExtent[e.Property.Name];
                }
            }

            // ---------------------------------------
            // We have seen the first nested SELECT statement, but not the column.
            var symbolPair = instanceSql as SymbolPair;
            if (symbolPair != null)
            {
                var columnJoinSymbol = symbolPair.Column as JoinSymbol;
                if (columnJoinSymbol != null)
                {
                    symbolPair.Column = columnJoinSymbol.NameToExtent[e.Property.Name];
                    return symbolPair;
                }
                else
                {
                    // symbolPair.Column has the base extent.
                    // we need the symbol for the column, since it might have been renamed
                    // when handling a JOIN.
                    if (symbolPair.Column.Columns.ContainsKey(e.Property.Name))
                    {
                        result = new SqlBuilder();
                        result.Append(symbolPair.Source);
                        result.Append(".");
                        var columnSymbol = symbolPair.Column.Columns[e.Property.Name];
                        optionalColumnUsageManager.MarkAsUsed(columnSymbol);
                        result.Append(columnSymbol);
                        return result;
                    }
                }
            }
            // ---------------------------------------

            result = new SqlBuilder();
            result.Append(instanceSql);
            result.Append(".");

            var symbol = instanceSql as Symbol;
            Symbol colSymbol;
            if (symbol != null
                && symbol.OutputColumns.TryGetValue(e.Property.Name, out colSymbol))
            {
                optionalColumnUsageManager.MarkAsUsed(colSymbol);
                if (symbol.OutputColumnsRenamed)
                {
                    result.Append(colSymbol);
                }
                else
                {
                    result.Append(QuoteIdentifier(e.Property.Name));
                }
            }
            else
            {
                // At this point the column name cannot be renamed, so we do
                // not use a symbol.
                result.Append(QuoteIdentifier(e.Property.Name));
            }
            return result;
        }

        // <summary>
        // Any(input, x) => Exists(Filter(input,x))
        // All(input, x) => Not Exists(Filter(input, not(x))
        // </summary>
        public override ISqlFragment Visit(DbQuantifierExpression e)
        {
            Check.NotNull(e, "e");

            var result = new SqlBuilder();

            var negatePredicate = (e.ExpressionKind == DbExpressionKind.All);
            if (e.ExpressionKind
                == DbExpressionKind.Any)
            {
                result.Append("EXISTS (");
            }
            else
            {
                Debug.Assert(e.ExpressionKind == DbExpressionKind.All);
                result.Append("NOT EXISTS (");
            }

            var filter = VisitFilterExpression(e.Input, e.Predicate, negatePredicate);
            if (filter.Select.IsEmpty)
            {
                AddDefaultColumns(filter);
            }

            result.Append(filter);
            result.Append(")");

            return result;
        }

        public override ISqlFragment Visit(DbRefExpression e)
        {
            Check.NotNull(e, "e");

            throw new NotSupportedException();
        }

        public override ISqlFragment Visit(DbRelationshipNavigationExpression e)
        {
            Check.NotNull(e, "e");

            throw new NotSupportedException();
        }

        // <summary>
        // For Sql9 it translates to:
        // SELECT Y.x1, Y.x2, ..., Y.xn
        // FROM (
        // SELECT X.x1, X.x2, ..., X.xn, row_number() OVER (ORDER BY sk1, sk2, ...) AS [row_number]
        // FROM input as X
        // ) as Y
        // WHERE Y.[row_number] > count
        // ORDER BY sk1, sk2, ...
        //
        // For Sql11 it translates to:
        // SELECT X.x1, X.x2, ..., X.xn
        // FROM input as X
        // ORDER BY sk1, sk2, ...
        // OFFSET s ROWS FETCH NEXT n ROWS ONLY
        // </summary>
        // <returns>
        // A <see cref="SqlBuilder" />
        // </returns>
        public override ISqlFragment Visit(DbSkipExpression e)
        {
            Check.NotNull(e, "e");

            Debug.Assert(SqlVersion != SqlVersion.Sql8, "DbSkipExpression when translating for SQL Server 2000.");

            Debug.Assert(
                e.Count is DbConstantExpression || e.Count is DbParameterReferenceExpression,
                "DbSkipExpression.Count is of invalid expression type");

            //Visit the input
            Symbol fromSymbol;
            var input = VisitInputExpression(e.Input.Expression, e.Input.VariableName, e.Input.VariableType, out fromSymbol);

            // Skip is not compatible with anything that OrderBy is not compatible with, as well as with distinct
            if (!IsCompatible(input, e.ExpressionKind))
            {
                input = CreateNewSelectStatement(input, e.Input.VariableName, e.Input.VariableType, out fromSymbol);
            }

            selectStatementStack.Push(input);
            symbolTable.EnterScope();

            AddFromSymbol(input, e.Input.VariableName, fromSymbol);

            if (SqlVersion >= SqlVersion.Sql11)
            {
                input.Select.Skip = new SkipClause(HandleCountExpression(e.Count));

                // Add the ORDER BY part.
                if (SqlProviderServices.UseRowNumberOrderingInOffsetQueries)
                {
                    input.OrderBy.Append("row_number() OVER (ORDER BY ");
                    AddSortKeys(input.OrderBy, e.SortOrder);
                    input.OrderBy.Append(")");
                }
                else
                {
                    AddSortKeys(input.OrderBy, e.SortOrder);
                }

                symbolTable.ExitScope();
                selectStatementStack.Pop();

                return input;
            }

            //Add the default columns
            Debug.Assert(input.Select.IsEmpty);
            var inputColumns = AddDefaultColumns(input);

            input.Select.Append("row_number() OVER (ORDER BY ");
            AddSortKeys(input.Select, e.SortOrder);
            input.Select.Append(") AS ");

            var row_numberName = "row_number";
            var row_numberSymbol = new Symbol(row_numberName, IntegerType);
            if (inputColumns.Any(c => String.Equals(c.Name, row_numberName, StringComparison.OrdinalIgnoreCase)))
            {
                row_numberSymbol.NeedsRenaming = true;
            }

            input.Select.Append(row_numberSymbol);

            //The inner statement is complete, its scopes need not be valid any longer
            symbolTable.ExitScope();
            selectStatementStack.Pop();

            //Create the resulting statement 
            //See CreateNewSelectStatement, it is very similar
            //Future Enhancement (katicad): Refactor to avoid duplication with CreateNewSelectStatement if we 
            // don't switch to using ExtensionExpression here
            var result = new SqlSelectStatement();
            result.From.Append("( ");
            result.From.Append(input);
            result.From.AppendLine();
            result.From.Append(") ");

            //Create a symbol for the input
            Symbol resultFromSymbol = null;

            if (input.FromExtents.Count == 1)
            {
                var oldJoinSymbol = input.FromExtents[0] as JoinSymbol;
                if (oldJoinSymbol != null)
                {
                    // Note: input.FromExtents will not do, since it might
                    // just be an alias of joinSymbol, and we want an actual JoinSymbol.
                    var newJoinSymbol = new JoinSymbol(e.Input.VariableName, e.Input.VariableType, oldJoinSymbol.ExtentList);
                    // This indicates that the oldStatement is a blocking scope
                    // i.e. it hides/renames extent columns
                    newJoinSymbol.IsNestedJoin = true;
                    newJoinSymbol.ColumnList = inputColumns;
                    newJoinSymbol.FlattenedExtentList = oldJoinSymbol.FlattenedExtentList;

                    resultFromSymbol = newJoinSymbol;
                }
            }

            if (resultFromSymbol == null)
            {
                // This is just a simple extent/SqlSelectStatement,
                // and we can get the column list from the type.
                resultFromSymbol = new Symbol(e.Input.VariableName, e.Input.VariableType, input.OutputColumns, false);
            }
            //Add the ORDER BY part
            selectStatementStack.Push(result);
            symbolTable.EnterScope();

            AddFromSymbol(result, e.Input.VariableName, resultFromSymbol);

            //Add the predicate 
            result.Where.Append(resultFromSymbol);
            result.Where.Append(".");
            result.Where.Append(row_numberSymbol);
            result.Where.Append(" > ");
            result.Where.Append(HandleCountExpression(e.Count));

            AddSortKeys(result.OrderBy, e.SortOrder);

            symbolTable.ExitScope();
            selectStatementStack.Pop();

            return result;
        }

        // <summary>
        // <see cref="Visit(DbFilterExpression)" />
        // </summary>
        // <returns>
        // A <see cref="SqlSelectStatement" />
        // </returns>
        // <seealso cref="Visit(DbFilterExpression)" />
        public override ISqlFragment Visit(DbSortExpression e)
        {
            Check.NotNull(e, "e");

            Symbol fromSymbol;
            var result = VisitInputExpression(e.Input.Expression, e.Input.VariableName, e.Input.VariableType, out fromSymbol);

            // OrderBy is compatible with Filter
            // and nothing else
            if (!IsCompatible(result, e.ExpressionKind))
            {
                result = CreateNewSelectStatement(result, e.Input.VariableName, e.Input.VariableType, out fromSymbol);
            }

            selectStatementStack.Push(result);
            symbolTable.EnterScope();

            AddFromSymbol(result, e.Input.VariableName, fromSymbol);

            AddSortKeys(result.OrderBy, e.SortOrder);

            symbolTable.ExitScope();
            selectStatementStack.Pop();

            return result;
        }

        // <returns>
        // A <see cref="SqlBuilder" />
        // </returns>
        public override ISqlFragment Visit(DbTreatExpression e)
        {
            Check.NotNull(e, "e");

            throw new NotSupportedException();
        }

        // <summary>
        // This code is shared by <see cref="Visit(DbExceptExpression)" />
        // and <see cref="Visit(DbIntersectExpression)" />
        // <see cref="VisitSetOpExpression" />
        // Since the left and right expression may not be Sql select statements,
        // we must wrap them up to look like SQL select statements.
        // </summary>
        public override ISqlFragment Visit(DbUnionAllExpression e)
        {
            Check.NotNull(e, "e");

            return VisitSetOpExpression(e, "UNION ALL");
        }

        // <summary>
        // This method determines whether an extent from an outer scope(free variable)
        // is used in the CurrentSelectStatement.
        // An extent in an outer scope, if its symbol is not in the FromExtents
        // of the CurrentSelectStatement.
        // </summary>
        // <returns>
        // A <see cref="Symbol" /> .
        // </returns>
        public override ISqlFragment Visit(DbVariableReferenceExpression e)
        {
            Check.NotNull(e, "e");

            if (isVarRefSingle)
            {
                throw new NotSupportedException();
                // A DbVariableReferenceExpression has to be a child of DbPropertyExpression or MethodExpression
                // This is also checked in GenerateSql(...) at the end of the visiting.
            }
            isVarRefSingle = true; // This will be reset by DbPropertyExpression or MethodExpression

            var result = symbolTable.Lookup(e.VariableName);
            optionalColumnUsageManager.MarkAsUsed(result);
            if (!CurrentSelectStatement.FromExtents.Contains(result))
            {
                CurrentSelectStatement.OuterExtents[result] = true;
            }

            return result;
        }

        // <summary>
        // Aggregates are not visited by the normal visitor walk.
        // </summary>
        // <param name="aggregate"> The aggregate go be translated </param>
        // <param name="aggregateArgument"> The translated aggregate argument </param>
        private static SqlBuilder VisitAggregate(DbAggregate aggregate, object aggregateArgument)
        {
            var aggregateResult = new SqlBuilder();
            var functionAggregate = aggregate as DbFunctionAggregate;

            if (functionAggregate == null)
            {
                throw new NotSupportedException();
            }

            //The only aggregate function with different name is Big_Count
            //Note: If another such function is to be added, a dictionary should be created
            if (functionAggregate.Function.IsCanonicalFunction()
                && String.Equals(functionAggregate.Function.Name, "BigCount", StringComparison.Ordinal))
            {
                aggregateResult.Append("COUNT_BIG");
            }
            else
            {
                SqlFunctionCallHandler.WriteFunctionName(aggregateResult, functionAggregate.Function);
            }

            aggregateResult.Append("(");

            var fnAggr = functionAggregate;
            if ((null != fnAggr)
                && (fnAggr.Distinct))
            {
                aggregateResult.Append("DISTINCT ");
            }

            aggregateResult.Append(aggregateArgument);

            aggregateResult.Append(")");
            return aggregateResult;
        }

        // <summary>
        // Dump out an expression - optionally wrap it with parantheses if possible
        // </summary>
        internal void ParenthesizeExpressionIfNeeded(DbExpression e, SqlBuilder result)
        {
            if (IsComplexExpression(e))
            {
                result.Append("(");
                result.Append(e.Accept(this));
                result.Append(")");
            }
            else
            {
                result.Append(e.Accept(this));
            }
        }

        // <summary>
        // Handler for inline binary expressions.
        // Produces left op right.
        // For associative operations does flattening.
        // Puts parenthesis around the arguments if needed.
        // </summary>
        private SqlBuilder VisitBinaryExpression(string op, DbExpressionKind expressionKind, DbExpression left, DbExpression right)
        {
            RemoveUnnecessaryCasts(ref left, ref right);

            var result = new SqlBuilder();

            var isFirst = true;
            foreach (var argument in FlattenAssociativeExpression(expressionKind, left, right))
            {
                if (isFirst)
                {
                    isFirst = false;
                }
                else
                {
                    result.Append(op);
                }
                ParenthesizeExpressionIfNeeded(argument, result);
            }
            return result;
        }

        // <summary>
        // Creates a flat list of the associative arguments.
        // For example, for ((A1 + (A2 - A3)) + A4) it will create A1, (A2 - A3), A4
        // Only 'unfolds' the given arguments that are of the given expression kind.
        // </summary>
        private static IEnumerable<DbExpression> FlattenAssociativeExpression(DbExpressionKind kind, DbExpression left, DbExpression right)
        {
            if (kind != DbExpressionKind.Or
                &&
                kind != DbExpressionKind.And
                &&
                kind != DbExpressionKind.Plus
                &&
                kind != DbExpressionKind.Multiply)
            {
                return new[] { left, right };
            }

            var argumentList = new List<DbExpression>();
            ExtractAssociativeArguments(kind, argumentList, left);
            ExtractAssociativeArguments(kind, argumentList, right);

            return argumentList;
        }

        // <summary>
        // Helper method for FlattenAssociativeExpression.
        // Creates a flat list of the associative arguments and appends to the given argument list.
        // For example, for ((A1 + (A2 - A3)) + A4) it will add A1, (A2 - A3), A4 to the list.
        // Only 'unfolds' the given expression if it is of the given expression kind.
        // </summary>
        private static void ExtractAssociativeArguments(
            DbExpressionKind expressionKind, List<DbExpression> argumentList, DbExpression expression)
        {
            var result =
                expression.GetLeafNodes(
                    expressionKind,
                    exp =>
                    {
                        //All associative expressions are binary, thus we must be dealing with a DbBinaryExpresson or 
                        // a DbArithmeticExpression with 2 arguments.
                        var binaryExpression = exp as DbBinaryExpression;
                        if (binaryExpression != null)
                        {
                            return new[] { binaryExpression.Left, binaryExpression.Right };
                        }
                        var arithmeticExpression = (DbArithmeticExpression)exp;
                        return arithmeticExpression.Arguments;
                    }
                    );

            argumentList.AddRange(result);
        }

        // <summary>
        // Private handler for comparison expressions - almost identical to VisitBinaryExpression.
        // We special case constants, so that we don't emit unnecessary casts
        // </summary>
        // <param name="op"> the comparison op </param>
        // <param name="left"> the left-side expression </param>
        // <param name="right"> the right-side expression </param>
        private SqlBuilder VisitComparisonExpression(string op, DbExpression left, DbExpression right)
        {
            RemoveUnnecessaryCasts(ref left, ref right);

            var result = new SqlBuilder();

            var isCastOptional = left.ResultType.EdmType == right.ResultType.EdmType;

            if (left.ExpressionKind
                == DbExpressionKind.Constant)
            {
                result.Append(VisitConstant((DbConstantExpression)left, isCastOptional));
            }
            else
            {
                ParenthesizeExpressionIfNeeded(left, result);
            }

            result.Append(op);

            if (right.ExpressionKind
                == DbExpressionKind.Constant)
            {
                result.Append(VisitConstant((DbConstantExpression)right, isCastOptional));
            }
            else
            {
                ParenthesizeExpressionIfNeeded(right, result);
            }

            return result;
        }

        private static void RemoveUnnecessaryCasts(ref DbExpression left, ref DbExpression right)
        {
            if (left.ResultType.EdmType != right.ResultType.EdmType)
            {
                return;
            }

            var leftCast = left as DbCastExpression;
            if (leftCast != null
                && leftCast.Argument.ResultType.EdmType == left.ResultType.EdmType)
            {
                left = leftCast.Argument;
            }

            var rightCast = right as DbCastExpression;
            if (rightCast != null
                && rightCast.Argument.ResultType.EdmType == left.ResultType.EdmType)
            {
                right = rightCast.Argument;
            }
        }

        // <summary>
        // This is called by the relational nodes.  It does the following
        // <list>
        //     <item>
        //         If the input is not a SqlSelectStatement, it assumes that the input
        //         is a collection expression, and creates a new SqlSelectStatement
        //     </item>
        // </list>
        // </summary>
        // <returns>
        // A <see cref="SqlSelectStatement" /> and the main fromSymbol for this select statement.
        // </returns>
        private SqlSelectStatement VisitInputExpression(
            DbExpression inputExpression,
            string inputVarName, TypeUsage inputVarType, out Symbol fromSymbol)
        {
            SqlSelectStatement result;
            var sqlFragment = inputExpression.Accept(this);
            result = sqlFragment as SqlSelectStatement;

            if (result == null)
            {
                result = new SqlSelectStatement();
                WrapNonQueryExtent(result, sqlFragment, inputExpression.ExpressionKind);
            }

            if (result.FromExtents.Count == 0)
            {
                // input was an extent
                fromSymbol = new Symbol(inputVarName, inputVarType);
            }
            else if (result.FromExtents.Count == 1)
            {
                // input was Filter/GroupBy/Project/OrderBy
                // we are likely to reuse this statement.
                fromSymbol = result.FromExtents[0];
            }
            else
            {
                // input was a join.
                // we are reusing the select statement produced by a Join node
                // we need to remove the original extents, and replace them with a
                // new extent with just the Join symbol.
                var joinSymbol = new JoinSymbol(inputVarName, inputVarType, result.FromExtents);
                joinSymbol.FlattenedExtentList = result.AllJoinExtents;

                fromSymbol = joinSymbol;
                result.FromExtents.Clear();
                result.FromExtents.Add(fromSymbol);
            }

            return result;
        }

        // <summary>
        // <see cref="Visit(DbIsEmptyExpression)" />
        // </summary>
        // <param name="negate"> Was the parent a DbNotExpression? </param>
        private SqlBuilder VisitIsEmptyExpression(DbIsEmptyExpression e, bool negate)
        {
            var result = new SqlBuilder();
            if (!negate)
            {
                result.Append(" NOT");
            }
            result.Append(" EXISTS (");
            result.Append(VisitExpressionEnsureSqlStatement(e.Argument));
            result.AppendLine();
            result.Append(")");

            return result;
        }

        // <summary>
        // Translate a NewInstance(Element(X)) expression into
        // "select top(1) * from X"
        // </summary>
        private ISqlFragment VisitCollectionConstructor(DbNewInstanceExpression e)
        {
            Debug.Assert(e.Arguments.Count <= 1);

            if (e.Arguments.Count == 1
                && e.Arguments[0].ExpressionKind == DbExpressionKind.Element)
            {
                var elementExpr = e.Arguments[0] as DbElementExpression;
                var result = VisitExpressionEnsureSqlStatement(elementExpr.Argument);

                if (!IsCompatible(result, DbExpressionKind.Element))
                {
                    Symbol fromSymbol;
                    var inputType = elementExpr.Argument.ResultType.GetElementTypeUsage();

                    result = CreateNewSelectStatement(result, "element", inputType, out fromSymbol);
                    AddFromSymbol(result, "element", fromSymbol, false);
                }
                result.Select.Top = new TopClause(1, false);
                return result;
            }

            // Otherwise simply build this out as a union-all ladder
            var collectionType = (CollectionType)e.ResultType.EdmType;
            Debug.Assert(collectionType != null);
            var isScalarElement = BuiltInTypeKind.PrimitiveType == collectionType.TypeUsage.EdmType.BuiltInTypeKind;

            var resultSql = new SqlBuilder();
            var separator = "";

            // handle empty table
            if (e.Arguments.Count == 0)
            {
                Debug.Assert(isScalarElement);
                resultSql.Append(" SELECT CAST(null as ");
                resultSql.Append(GetSqlPrimitiveType(collectionType.TypeUsage));
                resultSql.Append(") AS X FROM (SELECT 1) AS Y WHERE 1=0");
            }

            foreach (var arg in e.Arguments)
            {
                resultSql.Append(separator);
                resultSql.Append(" SELECT ");
                resultSql.Append(arg.Accept(this));
                // For scalar elements, no alias is appended yet. Add this.
                if (isScalarElement)
                {
                    resultSql.Append(" AS X ");
                }
                separator = " UNION ALL ";
            }

            return resultSql;
        }

        // <summary>
        // <see cref="Visit(DbIsNullExpression)" />
        // </summary>
        // <param name="negate"> Was the parent a DbNotExpression? </param>
        private SqlBuilder VisitIsNullExpression(DbIsNullExpression e, bool negate)
        {
            var result = new SqlBuilder();
            if (e.Argument.ExpressionKind
                == DbExpressionKind.ParameterReference)
            {
                _ignoreForceNonUnicodeFlag = true;
            }
            result.Append(e.Argument.Accept(this));
            // reset flag, it is not possible to reach this function with this flag set to true.
            _ignoreForceNonUnicodeFlag = false;
            if (!negate)
            {
                result.Append(" IS NULL");
            }
            else
            {
                result.Append(" IS NOT NULL");
            }

            return result;
        }

        // <summary>
        // This handles the processing of join expressions.
        // The extents on a left spine are flattened, while joins
        // not on the left spine give rise to new nested sub queries.
        // Joins work differently from the rest of the visiting, in that
        // the parent (i.e. the join node) creates the SqlSelectStatement
        // for the children to use.
        // The "parameter" IsInJoinContext indicates whether a child extent should
        // add its stuff to the existing SqlSelectStatement, or create a new SqlSelectStatement
        // By passing true, we ask the children to add themselves to the parent join,
        // by passing false, we ask the children to create new Select statements for
        // themselves.
        // This method is called from <see cref="Visit(DbApplyExpression)" /> and
        // <see cref="Visit(DbJoinExpression)" />.
        // </summary>
        // <returns>
        // A <see cref="SqlSelectStatement" />
        // </returns>
        private ISqlFragment VisitJoinExpression(
            IList<DbExpressionBinding> inputs, DbExpressionKind joinKind,
            string joinString, DbExpression joinCondition)
        {
            SqlSelectStatement result;
            // If the parent is not a join( or says that it is not),
            // we should create a new SqlSelectStatement.
            // otherwise, we add our child extents to the parent's FROM clause.
            if (!IsParentAJoin)
            {
                result = new SqlSelectStatement();
                result.AllJoinExtents = new List<Symbol>();
                selectStatementStack.Push(result);
            }
            else
            {
                result = CurrentSelectStatement;
            }

            // Process each of the inputs, and then the joinCondition if it exists.
            // It would be nice if we could call VisitInputExpression - that would
            // avoid some code duplication
            // but the Join postprocessing is messy and prevents this reuse.
            symbolTable.EnterScope();

            var separator = "";
            var isLeftMostInput = true;
            var inputCount = inputs.Count;
            for (var idx = 0; idx < inputCount; idx++)
            {
                var input = inputs[idx];

                if (separator.Length != 0)
                {
                    result.From.AppendLine();
                }
                result.From.Append(separator + " ");
                // Change this if other conditions are required
                // to force the child to produce a nested SqlStatement.
                var needsJoinContext = (input.Expression.ExpressionKind == DbExpressionKind.Scan)
                                       || (isLeftMostInput &&
                                           (IsJoinExpression(input.Expression)
                                            || IsApplyExpression(input.Expression)))
                    ;

                isParentAJoinStack.Push(needsJoinContext ? true : false);
                // if the child reuses our select statement, it will append the from
                // symbols to our FromExtents list.  So, we need to remember the
                // start of the child's entries.
                var fromSymbolStart = result.FromExtents.Count;

                var fromExtentFragment = input.Expression.Accept(this);

                isParentAJoinStack.Pop();

                ProcessJoinInputResult(fromExtentFragment, result, input, fromSymbolStart);
                separator = joinString;

                isLeftMostInput = false;
            }

            // Visit the on clause/join condition.
            switch (joinKind)
            {
                case DbExpressionKind.FullOuterJoin:
                case DbExpressionKind.InnerJoin:
                case DbExpressionKind.LeftOuterJoin:
                    result.From.Append(" ON ");
                    isParentAJoinStack.Push(false);
                    result.From.Append(joinCondition.Accept(this));
                    isParentAJoinStack.Pop();
                    break;
            }

            symbolTable.ExitScope();

            if (!IsParentAJoin)
            {
                selectStatementStack.Pop();
            }

            return result;
        }

        // <summary>
        // This is called from <see cref="VisitJoinExpression" />.
        // This is responsible for maintaining the symbol table after visiting
        // a child of a join expression.
        // The child's sql statement may need to be completed.
        // The child's result could be one of
        // <list type="number">
        //     <item>The same as the parent's - this is treated specially.</item>
        //     <item>A sql select statement, which may need to be completed</item>
        //     <item>An extent - just copy it to the from clause</item>
        //     <item>
        //         Anything else (from a collection-valued expression) -
        //         unnest and copy it.
        //     </item>
        // </list>
        // If the input was a Join, we need to create a new join symbol,
        // otherwise, we create a normal symbol.
        // We then call AddFromSymbol to add the AS clause, and update the symbol table.
        // If the child's result was the same as the parent's, we have to clean up
        // the list of symbols in the FromExtents list, since this contains symbols from
        // the children of both the parent and the child.
        // The happens when the child visited is a Join, and is the leftmost child of
        // the parent.
        // </summary>
        private void ProcessJoinInputResult(
            ISqlFragment fromExtentFragment, SqlSelectStatement result,
            DbExpressionBinding input, int fromSymbolStart)
        {
            Symbol fromSymbol = null;

            if (result != fromExtentFragment)
            {
                // The child has its own select statement, and is not reusing
                // our select statement.
                // This should look a lot like VisitInputExpression().
                var sqlSelectStatement = fromExtentFragment as SqlSelectStatement;
                if (sqlSelectStatement != null)
                {
                    if (sqlSelectStatement.Select.IsEmpty)
                    {
                        var columns = AddDefaultColumns(sqlSelectStatement);

                        if (IsJoinExpression(input.Expression)
                            || IsApplyExpression(input.Expression))
                        {
                            var extents = sqlSelectStatement.FromExtents;
                            var newJoinSymbol = new JoinSymbol(input.VariableName, input.VariableType, extents);
                            newJoinSymbol.IsNestedJoin = true;
                            newJoinSymbol.ColumnList = columns;

                            fromSymbol = newJoinSymbol;
                        }
                        else
                        {
                            // this is a copy of the code in CreateNewSelectStatement.

                            // if the oldStatement has a join as its input, ...
                            // clone the join symbol, so that we "reuse" the
                            // join symbol.  Normally, we create a new symbol - see the next block
                            // of code.
                            var oldJoinSymbol = sqlSelectStatement.FromExtents[0] as JoinSymbol;
                            if (oldJoinSymbol != null)
                            {
                                // Note: sqlSelectStatement.FromExtents will not do, since it might
                                // just be an alias of joinSymbol, and we want an actual JoinSymbol.
                                var newJoinSymbol = new JoinSymbol(input.VariableName, input.VariableType, oldJoinSymbol.ExtentList);
                                // This indicates that the sqlSelectStatement is a blocking scope
                                // i.e. it hides/renames extent columns
                                newJoinSymbol.IsNestedJoin = true;
                                newJoinSymbol.ColumnList = columns;
                                newJoinSymbol.FlattenedExtentList = oldJoinSymbol.FlattenedExtentList;

                                fromSymbol = newJoinSymbol;
                            }
                            else
                            {
                                fromSymbol = new Symbol(
                                    input.VariableName, input.VariableType, sqlSelectStatement.OutputColumns,
                                    sqlSelectStatement.OutputColumnsRenamed);
                            }
                        }
                    }
                    else
                    {
                        fromSymbol = new Symbol(
                            input.VariableName, input.VariableType, sqlSelectStatement.OutputColumns,
                            sqlSelectStatement.OutputColumnsRenamed);
                    }
                    result.From.Append(" (");
                    result.From.Append(sqlSelectStatement);
                    result.From.Append(" )");
                }
                else if (input.Expression is DbScanExpression)
                {
                    result.From.Append(fromExtentFragment);
                }
                else // bracket it
                {
                    WrapNonQueryExtent(result, fromExtentFragment, input.Expression.ExpressionKind);
                }

                if (fromSymbol == null) // i.e. not a join symbol
                {
                    fromSymbol = new Symbol(input.VariableName, input.VariableType);
                }

                AddFromSymbol(result, input.VariableName, fromSymbol);
                result.AllJoinExtents.Add(fromSymbol);
            }
            else // result == fromExtentFragment.  The child extents have been merged into the parent's.
            {
                // we are adding extents to the current sql statement via flattening.
                // We are replacing the child's extents with a single Join symbol.
                // The child's extents are all those following the index fromSymbolStart.
                //
                var extents = new List<Symbol>();

                // We cannot call extents.AddRange, since the is no simple way to
                // get the range of symbols fromSymbolStart..result.FromExtents.Count
                // from result.FromExtents.
                // We copy these symbols to create the JoinSymbol later.
                for (var i = fromSymbolStart; i < result.FromExtents.Count; ++i)
                {
                    extents.Add(result.FromExtents[i]);
                }
                result.FromExtents.RemoveRange(fromSymbolStart, result.FromExtents.Count - fromSymbolStart);
                fromSymbol = new JoinSymbol(input.VariableName, input.VariableType, extents);
                result.FromExtents.Add(fromSymbol);
                // this Join Symbol does not have its own select statement, so we
                // do not set IsNestedJoin

                // We do not call AddFromSymbol(), since we do not want to add
                // "AS alias" to the FROM clause- it has been done when the extent was added earlier.
                symbolTable.Add(input.VariableName, fromSymbol);
            }
        }

        // <summary>
        // We assume that this is only called as a child of a Project.
        // This replaces <see cref="Visit(DbNewInstanceExpression)" />, since
        // we do not allow DbNewInstanceExpression as a child of any node other than
        // DbProjectExpression.
        // We write out the translation of each of the columns in the record.
        // </summary>
        // <returns>
        // A <see cref="SqlBuilder" />
        // </returns>
        private ISqlFragment VisitNewInstanceExpression(
            DbNewInstanceExpression e, bool aliasesNeedRenaming, out Dictionary<string, Symbol> newColumns)
        {
            var result = new SqlBuilder();
            var rowType = e.ResultType.EdmType as RowType;

            if (null != rowType)
            {
                newColumns = new Dictionary<string, Symbol>(e.Arguments.Count);

                var members = rowType.Properties;
                var separator = "";
                for (var i = 0; i < e.Arguments.Count; ++i)
                {
                    var argument = e.Arguments[i];
                    if (BuiltInTypeKind.RowType
                        == argument.ResultType.EdmType.BuiltInTypeKind)
                    {
                        // We do not support nested records or other complex objects.
                        throw new NotSupportedException();
                    }

                    var member = members[i];
                    result.Append(separator);
                    result.AppendLine();
                    result.Append(argument.Accept(this));
                    result.Append(" AS ");
                    if (aliasesNeedRenaming)
                    {
                        var column = new Symbol(member.Name, member.TypeUsage);
                        column.NeedsRenaming = true;
                        column.NewName = String.Concat("Internal_", member.Name);
                        result.Append(column);
                        newColumns.Add(member.Name, column);
                    }
                    else
                    {
                        result.Append(QuoteIdentifier(member.Name));
                    }
                    separator = ", ";
                }
            }
            else
            {
                //
                // CONSIDER revisiting other possible expressions such as NominalTypes. for the time being
                // types other then RowType (such as UDTs for instance) are not supported.
                //
                throw new NotSupportedException();
            }

            return result;
        }

        // <summary>
        // Handler for set operations
        // It generates left separator right.
        // Only for SQL 8.0 it may need to create a new select statement
        // above the set operation if the left child's output columns got renamed
        // </summary>
        private ISqlFragment VisitSetOpExpression(DbBinaryExpression setOpExpression, string separator)
        {
            var leafSelectStatements = new List<SqlSelectStatement>();
            VisitAndGatherSetOpLeafExpressions(setOpExpression.ExpressionKind, setOpExpression.Left, leafSelectStatements);
            VisitAndGatherSetOpLeafExpressions(setOpExpression.ExpressionKind, setOpExpression.Right, leafSelectStatements);

            var setStatement = new SqlBuilder();

            for (var i = 0; i < leafSelectStatements.Count; ++i)
            {
                if (i > 0)
                {
                    setStatement.AppendLine();
                    setStatement.Append(separator); // e.g. UNION ALL
                    setStatement.AppendLine();
                }
                setStatement.Append(leafSelectStatements[i]);  
            }

            //This is the common scenario
            if (!leafSelectStatements[0].OutputColumnsRenamed)
            {
                return setStatement;
            }
            else
            {
                // This is case only for SQL 8.0 when the left child has order by in it
                // If the output columns of the left child got renamed, 
                // then the output of the union all is renamed
                // All this currenlty only happens for UNION ALL, because INTERSECT and
                // EXCEPT get translated for SQL 8.0 before SqlGen.
                var selectStatement = new SqlSelectStatement();
                selectStatement.From.Append("( ");
                selectStatement.From.Append(setStatement);
                selectStatement.From.AppendLine();
                selectStatement.From.Append(") ");

                var fromSymbol = new Symbol("X", setOpExpression.Left.ResultType.GetElementTypeUsage(), leafSelectStatements[0].OutputColumns, true);
                AddFromSymbol(selectStatement, null, fromSymbol, false);

                return selectStatement;
            }
        }

        // <summary>
        // Visits the given expression, expanding nodes of type kind and collecting all visited leaf nodes in leafSelectStatements.
        // The purpose of this is to flatten UNION ALL and INTERSECT statements to avoid deep nesting.
        // </summary>
        // <param name="kind">the kind of expression matching the tree we're visiting</param>
        // <param name="expression">the expression to visit</param>
        // <param name="leafSelectStatements">accumulator for the collected leaf select statements</param>
        private void VisitAndGatherSetOpLeafExpressions(DbExpressionKind kind, DbExpression expression, List<SqlSelectStatement> leafSelectStatements)
        {
            // only allow deep flattening of set op trees when
            // (1) we are newer than Sql 8.0 (since it needs special handling for set ops anyway... see VisitSetOpExpression)
            if (this.SqlVersion > SqlVersion.Sql8
                // (2) we are UNION ALL or INTERSECT (EXCEPT is not safe to flatten since it is order-dependent)
                && (kind == DbExpressionKind.UnionAll || kind == DbExpressionKind.Intersect)
                // (3) the given expression is another instance of the given kind
                && expression.ExpressionKind == kind)
            {
                var binary = (DbBinaryExpression)expression;
                VisitAndGatherSetOpLeafExpressions(kind, binary.Left, leafSelectStatements);
                VisitAndGatherSetOpLeafExpressions(kind, binary.Right, leafSelectStatements);
            }
            else
            {
                leafSelectStatements.Add(VisitExpressionEnsureSqlStatement(expression, true, true));
            }
        }

        // <summary>
        // <see cref="AddDefaultColumns" />
        // Add the column names from the referenced extent/join to the
        // select statement.
        // If the symbol is a JoinSymbol, we recursively visit all the extents,
        // halting at real extents and JoinSymbols that have an associated SqlSelectStatement.
        // The column names for a real extent can be derived from its type.
        // The column names for a Join Select statement can be got from the
        // list of columns that was created when the Join's select statement
        // was created.
        // We do the following for each column.
        // <list type="number">
        //     <item>Add the SQL string for each column to the SELECT clause</item>
        //     <item>
        //         Add the column to the list of columns - so that it can
        //         become part of the "type" of a JoinSymbol
        //     </item>
        //     <item>
        //         Check if the column name collides with a previous column added
        //         to the same select statement.  Flag both the columns for renaming if true.
        //     </item>
        //     <item>Add the column to a name lookup dictionary for collision detection.</item>
        // </list>
        // </summary>
        // <param name="selectStatement"> The select statement that started off as SELECT * </param>
        // <param name="symbol"> The symbol containing the type information for the columns to be added. </param>
        // <param name="columnList">
        // Columns that have been added to the Select statement. This is created in
        // <see
        //     cref="AddDefaultColumns" />
        // .
        // </param>
        // <param name="columnDictionary"> A dictionary of the columns above. </param>
        private void AddColumns(
            SqlSelectStatement selectStatement, Symbol symbol,
            List<Symbol> columnList, Dictionary<string, Symbol> columnDictionary)
        {
            var joinSymbol = symbol as JoinSymbol;
            if (joinSymbol != null)
            {
                if (!joinSymbol.IsNestedJoin)
                {
                    // Recurse if the join symbol is a collection of flattened extents
                    foreach (var sym in joinSymbol.ExtentList)
                    {
                        // if sym is ScalarType means we are at base case in the
                        // recursion and there are not columns to add, just skip
                        if ((sym.Type == null)
                            || BuiltInTypeKind.PrimitiveType == sym.Type.EdmType.BuiltInTypeKind)
                        {
                            continue;
                        }

                        AddColumns(selectStatement, sym, columnList, columnDictionary);
                    }
                }
                else
                {
                    foreach (var joinColumn in joinSymbol.ColumnList)
                    {
                        // we write tableName.columnName
                        // rather than tableName.columnName as alias
                        // since the column name is unique (by the way we generate new column names)
                        //
                        // We use the symbols for both the table and the column,
                        // since they are subject to renaming.

                        //This is called from AddDefaultColumns. To avoid adding columns that may not be used later,
                        // we add an optional column, that will only be added if needed.
                        var optionalColumn = CreateOptionalColumn(null, joinColumn);

                        optionalColumn.Append(symbol);
                        optionalColumn.Append(".");
                        optionalColumn.Append(joinColumn);

                        selectStatement.Select.AddOptionalColumn(optionalColumn);

                        // check for name collisions.  If there is,
                        // flag both the colliding symbols.
                        if (columnDictionary.ContainsKey(joinColumn.Name))
                        {
                            columnDictionary[joinColumn.Name].NeedsRenaming = true; // the original symbol
                            joinColumn.NeedsRenaming = true; // the current symbol.
                        }
                        else
                        {
                            columnDictionary[joinColumn.Name] = joinColumn;
                        }

                        columnList.Add(joinColumn);
                    }
                }
            }
            else
            {
                // This is a non-join extent/select statement, and the CQT type has
                // the relevant column information.

                // The type could be a record type(e.g. Project(...),
                // or an entity type ( e.g. EntityExpression(...)
                // so, we check whether it is a structuralType.

                // Consider an expression of the form J(a, b=P(E))
                // The inner P(E) would have been translated to a SQL statement
                // We should not use the raw names from the type, but the equivalent
                // symbols (they are present in symbol.Columns) if they exist.
                //
                // We add the new columns to the symbol's columns if they do
                // not already exist.
                //
                // If the symbol represents a SqlStatement with renamed output columns,
                // we should use these instead of the rawnames and we should also mark
                // this selectStatement as one with renamed columns

                if (symbol.OutputColumnsRenamed)
                {
                    selectStatement.OutputColumnsRenamed = true;
                }

                if (selectStatement.OutputColumns == null)
                {
                    selectStatement.OutputColumns = new Dictionary<string, Symbol>();
                }

                if ((symbol.Type == null)
                    || BuiltInTypeKind.PrimitiveType == symbol.Type.EdmType.BuiltInTypeKind)
                {
                    AddColumn(selectStatement, symbol, columnList, columnDictionary, "X");
                }
                else
                {
                    foreach (var property in symbol.Type.GetProperties())
                    {
                        AddColumn(selectStatement, symbol, columnList, columnDictionary, property.Name);
                    }
                }
            }
        }

        // <summary>
        // Creates an optional column and registers the corresponding symbol with
        // the optionalColumnUsageManager it has not already been registered.
        // </summary>
        private OptionalColumn CreateOptionalColumn(Symbol inputColumnSymbol, Symbol column)
        {
            if (!optionalColumnUsageManager.ContainsKey(column))
            {
                optionalColumnUsageManager.Add(inputColumnSymbol, column);
            }
            return new OptionalColumn(optionalColumnUsageManager, column);
        }

        // <summary>
        // Helper method for AddColumns. Adds a column with the given column name
        // to the Select list of the given select statement.
        // </summary>
        // <param name="selectStatement"> The select statement to whose SELECT part the column should be added </param>
        // <param name="symbol"> The symbol from which the column to be added originated </param>
        // <param name="columnList">
        // Columns that have been added to the Select statement. This is created in
        // <see
        //     cref="AddDefaultColumns" />
        // .
        // </param>
        // <param name="columnDictionary"> A dictionary of the columns above. </param>
        // <param name="columnName"> The name of the column to be added. </param>
        private void AddColumn(
            SqlSelectStatement selectStatement, Symbol symbol,
            List<Symbol> columnList, Dictionary<string, Symbol> columnDictionary, string columnName)
        {
            // Since all renaming happens in the second phase
            // we lose nothing by setting the next column name index to 0
            // many times.
            allColumnNames[columnName] = 0;

            Symbol inputSymbol = null;
            symbol.OutputColumns.TryGetValue(columnName, out inputSymbol);

            // Create a new symbol/reuse existing symbol for the column
            Symbol columnSymbol;
            if (!symbol.Columns.TryGetValue(columnName, out columnSymbol))
            {
                // we do not care about the types of columns, so we pass null
                // when construction the symbol.
                columnSymbol = ((inputSymbol != null) && symbol.OutputColumnsRenamed) ? inputSymbol : new Symbol(columnName, null);
                symbol.Columns.Add(columnName, columnSymbol);
            }

            var optionalColumn = CreateOptionalColumn(inputSymbol, columnSymbol);

            optionalColumn.Append(symbol);
            optionalColumn.Append(".");

            if (symbol.OutputColumnsRenamed)
            {
                optionalColumn.Append(inputSymbol);
            }
            else
            {
                optionalColumn.Append(QuoteIdentifier(columnName));
            }

            optionalColumn.Append(" AS ");
            optionalColumn.Append(columnSymbol);

            selectStatement.Select.AddOptionalColumn(optionalColumn);

            //If the columnName is already in the output columns, it means it is being tracked
            // via the join symbol mechanism
            if (!selectStatement.OutputColumns.ContainsKey(columnName))
            {
                selectStatement.OutputColumns.Add(columnName, columnSymbol);
            }

            // Check for column name collisions.
            if (columnDictionary.ContainsKey(columnName))
            {
                columnDictionary[columnName].NeedsRenaming = true;
                columnSymbol.NeedsRenaming = true;
            }
            else
            {
                columnDictionary[columnName] = symbol.Columns[columnName];
            }

            columnList.Add(columnSymbol);
        }

        // <summary>
        // Expands Select * to "select the_list_of_columns"
        // If the columns are taken from an extent, they are written as
        // {original_column_name AS Symbol(original_column)} to allow renaming.
        // If the columns are taken from a Join, they are written as just
        // {original_column_name}, since there cannot be a name collision.
        // We concatenate the columns from each of the inputs to the select statement.
        // Since the inputs may be joins that are flattened, we need to recurse.
        // The inputs are inferred from the symbols in FromExtents.
        // </summary>
        private List<Symbol> AddDefaultColumns(SqlSelectStatement selectStatement)
        {
            // This is the list of columns added in this select statement
            // This forms the "type" of the Select statement, if it has to
            // be expanded in another SELECT *
            var columnList = new List<Symbol>();

            // A lookup for the previous set of columns to aid column name
            // collision detection.
            var columnDictionary = new Dictionary<string, Symbol>(StringComparer.OrdinalIgnoreCase);

            foreach (var symbol in selectStatement.FromExtents)
            {
                AddColumns(selectStatement, symbol, columnList, columnDictionary);
            }

            return columnList;
        }

        // <summary>
        // <see cref="AddFromSymbol(SqlSelectStatement, string, Symbol, bool)" />
        // </summary>
        private void AddFromSymbol(SqlSelectStatement selectStatement, string inputVarName, Symbol fromSymbol)
        {
            AddFromSymbol(selectStatement, inputVarName, fromSymbol, true);
        }

        // <summary>
        // This method is called after the input to a relational node is visited.
        // <see cref="Visit(DbProjectExpression)" /> and <see cref="ProcessJoinInputResult" />
        // There are 2 scenarios
        // <list type="number">
        //     <item>
        //         The fromSymbol is new i.e. the select statement has just been
        //         created, or a join extent has been added.
        //     </item>
        //     <item>The fromSymbol is old i.e. we are reusing a select statement.</item>
        // </list>
        // If we are not reusing the select statement, we have to complete the
        // FROM clause with the alias
        // <code>-- if the input was an extent
        //     FROM = [SchemaName].[TableName]
        //     -- if the input was a Project
        //     FROM = (SELECT ... FROM ... WHERE ...)</code>
        // These become
        // <code>-- if the input was an extent
        //     FROM = [SchemaName].[TableName] AS alias
        //     -- if the input was a Project
        //     FROM = (SELECT ... FROM ... WHERE ...) AS alias</code>
        // and look like valid FROM clauses.
        // Finally, we have to add the alias to the global list of aliases used,
        // and also to the current symbol table.
        // </summary>
        // <param name="inputVarName"> The alias to be used. </param>
        private void AddFromSymbol(SqlSelectStatement selectStatement, string inputVarName, Symbol fromSymbol, bool addToSymbolTable)
        {
            // the first check is true if this is a new statement
            // the second check is true if we are in a join - we do not
            // check if we are in a join context.
            // We do not want to add "AS alias" if it has been done already
            // e.g. when we are reusing the Sql statement.
            if (selectStatement.FromExtents.Count == 0
                || fromSymbol != selectStatement.FromExtents[0])
            {
                selectStatement.FromExtents.Add(fromSymbol);
                selectStatement.From.Append(" AS ");
                selectStatement.From.Append(fromSymbol);

                // We have this inside the if statement, since
                // we only want to add extents that are actually used.
                allExtentNames[fromSymbol.Name] = 0;
            }

            if (addToSymbolTable)
            {
                symbolTable.Add(inputVarName, fromSymbol);
            }
        }

        // <summary>
        // Translates a list of SortClauses.
        // Used in the translation of OrderBy
        // </summary>
        // <param name="orderByClause"> The SqlBuilder to which the sort keys should be appended </param>
        private void AddSortKeys(SqlBuilder orderByClause, IList<DbSortClause> sortKeys)
        {
            var separator = "";
            foreach (var sortClause in sortKeys)
            {
                orderByClause.Append(separator);
                orderByClause.Append(sortClause.Expression.Accept(this));
                // Bug 431021: COLLATE clause must precede ASC/DESC
                Debug.Assert(sortClause.Collation != null);
                if (!String.IsNullOrEmpty(sortClause.Collation))
                {
                    orderByClause.Append(" COLLATE ");
                    orderByClause.Append(sortClause.Collation);
                }

                orderByClause.Append(sortClause.Ascending ? " ASC" : " DESC");

                separator = ", ";
            }
        }

        // <summary>
        // <see cref="CreateNewSelectStatement(SqlSelectStatement, string, TypeUsage, bool, out Symbol)" />
        // </summary>
        private SqlSelectStatement CreateNewSelectStatement(
            SqlSelectStatement oldStatement,
            string inputVarName, TypeUsage inputVarType, out Symbol fromSymbol)
        {
            return CreateNewSelectStatement(oldStatement, inputVarName, inputVarType, true, out fromSymbol);
        }

        // <summary>
        // This is called after a relational node's input has been visited, and the
        // input's sql statement cannot be reused.  <see cref="Visit(DbProjectExpression)" />
        // When the input's sql statement cannot be reused, we create a new sql
        // statement, with the old one as the from clause of the new statement.
        // The old statement must be completed i.e. if it has an empty select list,
        // the list of columns must be projected out.
        // If the old statement being completed has a join symbol as its from extent,
        // the new statement must have a clone of the join symbol as its extent.
        // We cannot reuse the old symbol, but the new select statement must behave
        // as though it is working over the "join" record.
        // </summary>
        // <returns> A new select statement, with the old one as the from clause. </returns>
        private SqlSelectStatement CreateNewSelectStatement(
            SqlSelectStatement oldStatement,
            string inputVarName, TypeUsage inputVarType, bool finalizeOldStatement, out Symbol fromSymbol)
        {
            fromSymbol = null;

            // Finalize the old statement
            if (finalizeOldStatement && oldStatement.Select.IsEmpty)
            {
                var columns = AddDefaultColumns(oldStatement);

                // Thid could not have been called from a join node.
                Debug.Assert(oldStatement.FromExtents.Count == 1);

                // if the oldStatement has a join as its input, ...
                // clone the join symbol, so that we "reuse" the
                // join symbol.  Normally, we create a new symbol - see the next block
                // of code.
                var oldJoinSymbol = oldStatement.FromExtents[0] as JoinSymbol;
                if (oldJoinSymbol != null)
                {
                    // Note: oldStatement.FromExtents will not do, since it might
                    // just be an alias of joinSymbol, and we want an actual JoinSymbol.
                    var newJoinSymbol = new JoinSymbol(inputVarName, inputVarType, oldJoinSymbol.ExtentList);
                    // This indicates that the oldStatement is a blocking scope
                    // i.e. it hides/renames extent columns
                    newJoinSymbol.IsNestedJoin = true;
                    newJoinSymbol.ColumnList = columns;
                    newJoinSymbol.FlattenedExtentList = oldJoinSymbol.FlattenedExtentList;

                    fromSymbol = newJoinSymbol;
                }
            }

            if (fromSymbol == null)
            {
                fromSymbol = new Symbol(inputVarName, inputVarType, oldStatement.OutputColumns, oldStatement.OutputColumnsRenamed);
            }

            // Observe that the following looks like the body of Visit(ExtentExpression).
            var selectStatement = new SqlSelectStatement();
            selectStatement.From.Append("( ");
            selectStatement.From.Append(oldStatement);
            selectStatement.From.AppendLine();
            selectStatement.From.Append(") ");

            return selectStatement;
        }

        // <summary>
        // Before we embed a string literal in a SQL string, we should
        // convert all ' to '', and enclose the whole string in single quotes.
        // </summary>
        // <returns> The escaped sql string. </returns>
        private static string EscapeSingleQuote(string s, bool isUnicode)
        {
            return (isUnicode ? "N'" : "'") + s.Replace("'", "''") + "'";
        }

        // <summary>
        // Returns the sql primitive/native type name.
        // It will include size, precision or scale depending on type information present in the
        // type facets
        // </summary>
        private string GetSqlPrimitiveType(TypeUsage type)
        {
            Debug.Assert(type.EdmType.GetMetadataPropertyValue<DataSpace>("DataSpace") == DataSpace.CSpace);

            var storeTypeUsage = _storeItemCollection.ProviderManifest.GetStoreType(type);
            return GenerateSqlForStoreType(_sqlVersion, storeTypeUsage);
        }

        internal static string GenerateSqlForStoreType(SqlVersion sqlVersion, TypeUsage storeTypeUsage)
        {
            Debug.Assert(BuiltInTypeKind.PrimitiveType == storeTypeUsage.EdmType.BuiltInTypeKind, "Type must be primitive type");

            var typeName = storeTypeUsage.EdmType.Name;
            var hasFacet = false;
            var maxLength = 0;
            byte decimalPrecision = 0;
            byte decimalScale = 0;

            var primitiveTypeKind = ((PrimitiveType)storeTypeUsage.EdmType).PrimitiveTypeKind;

            switch (primitiveTypeKind)
            {
                case PrimitiveTypeKind.Binary:
                    if (!storeTypeUsage.MustFacetBeConstant(DbProviderManifest.MaxLengthFacetName))
                    {
                        hasFacet = storeTypeUsage.TryGetMaxLength(out maxLength);
                        Debug.Assert(hasFacet, "Binary type did not have MaxLength facet");
                        typeName = typeName + "(" + maxLength.ToString(CultureInfo.InvariantCulture) + ")";
                    }
                    break;

                case PrimitiveTypeKind.String:
                    if (!storeTypeUsage.MustFacetBeConstant(DbProviderManifest.MaxLengthFacetName))
                    {
                        hasFacet = storeTypeUsage.TryGetMaxLength(out maxLength);
                        Debug.Assert(hasFacet, "String type did not have MaxLength facet");
                        typeName = typeName + "(" + maxLength.ToString(CultureInfo.InvariantCulture) + ")";
                    }
                    break;

                case PrimitiveTypeKind.DateTime:
                    typeName = SqlVersionUtils.IsPreKatmai(sqlVersion) ? "datetime" : "datetime2";
                    break;
                case PrimitiveTypeKind.Time:
                    AssertKatmaiOrNewer(sqlVersion, primitiveTypeKind);
                    typeName = "time";
                    break;
                case PrimitiveTypeKind.DateTimeOffset:
                    AssertKatmaiOrNewer(sqlVersion, primitiveTypeKind);
                    typeName = "datetimeoffset";
                    break;

                case PrimitiveTypeKind.Decimal:
                    if (!storeTypeUsage.MustFacetBeConstant(DbProviderManifest.PrecisionFacetName))
                    {
                        hasFacet = storeTypeUsage.TryGetPrecision(out decimalPrecision);
                        Debug.Assert(hasFacet, "decimal must have precision facet");
                        Debug.Assert(decimalPrecision > 0, "decimal precision must be greater than zero");
                        hasFacet = storeTypeUsage.TryGetScale(out decimalScale);
                        Debug.Assert(hasFacet, "decimal must have scale facet");
                        Debug.Assert(decimalPrecision >= decimalScale, "decimalPrecision must be greater or equal to decimalScale");
                        typeName = typeName + "(" + decimalPrecision + "," + decimalScale + ")";
                    }
                    break;

                default:
                    break;
            }

            return typeName;
        }

        // <summary>
        // Handles the expression represending DbLimitExpression.Limit and DbSkipExpression.Count.
        // If it is a constant expression, it simply does to string thus avoiding casting it to the specific value
        // (which would be done if <see cref="Visit(DbConstantExpression)" /> is called)
        // </summary>
        private ISqlFragment HandleCountExpression(DbExpression e)
        {
            ISqlFragment result;

            if (e.ExpressionKind
                == DbExpressionKind.Constant)
            {
                //For constant expression we should not cast the value, 
                // thus we don't go throught the default DbConstantExpression handling
                var sqlBuilder = new SqlBuilder();
                sqlBuilder.Append(((DbConstantExpression)e).Value.ToString());
                result = sqlBuilder;
            }
            else
            {
                result = e.Accept(this);
            }

            return result;
        }

        // <summary>
        // This is used to determine if a particular expression is an Apply operation.
        // This is only the case when the DbExpressionKind is CrossApply or OuterApply.
        // </summary>
        private static bool IsApplyExpression(DbExpression e)
        {
            return (DbExpressionKind.CrossApply == e.ExpressionKind || DbExpressionKind.OuterApply == e.ExpressionKind);
        }

        // <summary>
        // This is used to determine if a particular expression is a Join operation.
        // This is true for DbCrossJoinExpression and DbJoinExpression, the
        // latter of which may have one of several different ExpressionKinds.
        // </summary>
        private static bool IsJoinExpression(DbExpression e)
        {
            return (DbExpressionKind.CrossJoin == e.ExpressionKind ||
                    DbExpressionKind.FullOuterJoin == e.ExpressionKind ||
                    DbExpressionKind.InnerJoin == e.ExpressionKind ||
                    DbExpressionKind.LeftOuterJoin == e.ExpressionKind);
        }

        // <summary>
        // This is used to determine if a calling expression needs to place
        // round brackets around the translation of the expression e.
        // Constants, parameters and properties do not require brackets,
        // everything else does.
        // </summary>
        // <returns> true, if the expression needs brackets </returns>
        private static bool IsComplexExpression(DbExpression e)
        {
            switch (e.ExpressionKind)
            {
                case DbExpressionKind.Constant:
                case DbExpressionKind.ParameterReference:
                case DbExpressionKind.Property:
                case DbExpressionKind.Cast:
                    return false;

                default:
                    return true;
            }
        }

        // <summary>
        // Determine if the owner expression can add its unique sql to the input's
        // SqlSelectStatement
        // </summary>
        // <param name="result"> The SqlSelectStatement of the input to the relational node. </param>
        // <param name="expressionKind"> The kind of the expression node(not the input's) </param>
        [SuppressMessage("Microsoft.Maintainability", "CA1502:AvoidExcessiveComplexity")]
        private static bool IsCompatible(SqlSelectStatement result, DbExpressionKind expressionKind)
        {
            switch (expressionKind)
            {
                case DbExpressionKind.Distinct:
                    return result.Select.Top == null
                           && result.Select.Skip == null
                        // #494803: The projection after distinct may not project all 
                        // columns used in the Order By
                        // Improvement: Consider getting rid of the Order By instead
                           && result.OrderBy.IsEmpty;

                case DbExpressionKind.Filter:
                    return result.Select.IsEmpty
                           && result.Where.IsEmpty
                           && result.GroupBy.IsEmpty
                           && result.Select.Top == null
                           && result.Select.Skip == null;

                case DbExpressionKind.GroupBy:
                    return result.Select.IsEmpty
                           && result.GroupBy.IsEmpty
                           && result.OrderBy.IsEmpty
                           && result.Select.Top == null
                           && result.Select.Skip == null
                           && !result.Select.IsDistinct;

                case DbExpressionKind.Limit:
                case DbExpressionKind.Element:
                    return result.Select.Top == null;

                case DbExpressionKind.Project:
                    // SQLBUDT #427998: Allow a Project to be compatible with an OrderBy
                    // Otherwise we won't be able to sort an input, and project out only
                    // a subset of the input columns
                    return result.Select.IsEmpty
                           && result.GroupBy.IsEmpty
                        // SQLBUDT #513640 - If distinct is specified, the projection may affect
                        // the cardinality of the results, thus a new statement must be started.
                           && !result.Select.IsDistinct;

                case DbExpressionKind.Skip:
                    return result.Select.IsEmpty
                           && result.Select.Skip == null
                           && result.GroupBy.IsEmpty
                           && result.OrderBy.IsEmpty
                           && !result.Select.IsDistinct;

                case DbExpressionKind.Sort:
                    return result.Select.IsEmpty
                           && result.GroupBy.IsEmpty
                           && result.OrderBy.IsEmpty
                        // SQLBUDT #513640 - A Project may be on the top of the Sort, and if so, it would need
                        // to be in the same statement as the Sort (see comment above for the Project case).
                        // A Distinct in the same statement would prevent that, and therefore if Distinct is present,
                        // we need to start a new statement. 
                           && !result.Select.IsDistinct;

                default:
                    Debug.Assert(false);
                    throw new InvalidOperationException(String.Empty);
            }
        }

        // <summary>
        // We use the normal box quotes for SQL server.  We do not deal with ANSI quotes
        // i.e. double quotes.
        // </summary>
        internal static string QuoteIdentifier(string name)
        {
            DebugCheck.NotEmpty(name);
            // We assume that the names are not quoted to begin with.
            return "[" + name.Replace("]", "]]") + "]";
        }

        // <summary>
        // Simply calls <see cref="VisitExpressionEnsureSqlStatement(DbExpression, bool, bool)" />
        // with addDefaultColumns set to true and markAllDefaultColumnsAsUsed set to false.
        // </summary>
        private SqlSelectStatement VisitExpressionEnsureSqlStatement(DbExpression e)
        {
            return VisitExpressionEnsureSqlStatement(e, true, false);
        }

        // <summary>
        // This is called from <see cref="GenerateSql(DbQueryCommandTree, out HashSet{string})" />
        // and nodes which require a select statement as an argument e.g. <see cref="Visit(DbIsEmptyExpression)" />,
        // <see cref="Visit(DbUnionAllExpression)" />.
        // SqlGenerator needs its child to have a proper alias if the child is
        // just an extent or a join.
        // The normal relational nodes result in complete valid SQL statements.
        // For the rest, we need to treat them as there was a dummy
        // <code>-- originally {expression}
        //                                 -- change that to
        //                                 SELECT *
        //                                 FROM {expression} as c</code>
        // DbLimitExpression needs to start the statement but not add the default columns
        // </summary>
        private SqlSelectStatement VisitExpressionEnsureSqlStatement(
            DbExpression e, bool addDefaultColumns, bool markAllDefaultColumnsAsUsed)
        {
            Debug.Assert(BuiltInTypeKind.CollectionType == e.ResultType.EdmType.BuiltInTypeKind);

            SqlSelectStatement result;
            switch (e.ExpressionKind)
            {
                case DbExpressionKind.Project:
                case DbExpressionKind.Filter:
                case DbExpressionKind.GroupBy:
                case DbExpressionKind.Sort:
                    result = e.Accept(this) as SqlSelectStatement;
                    break;

                default:
                    Symbol fromSymbol;
                    var inputVarName = "c"; // any name will do - this is my random choice.
                    symbolTable.EnterScope();

                    TypeUsage type = null;
                    switch (e.ExpressionKind)
                    {
                        case DbExpressionKind.Scan:
                        case DbExpressionKind.CrossJoin:
                        case DbExpressionKind.FullOuterJoin:
                        case DbExpressionKind.InnerJoin:
                        case DbExpressionKind.LeftOuterJoin:
                        case DbExpressionKind.CrossApply:
                        case DbExpressionKind.OuterApply:
                            // #490026: It used to be type = e.ResultType. 
                            type = e.ResultType.GetElementTypeUsage();
                            break;

                        default:
                            Debug.Assert(BuiltInTypeKind.CollectionType == e.ResultType.EdmType.BuiltInTypeKind);
                            type = ((CollectionType)e.ResultType.EdmType).TypeUsage;
                            break;
                    }

                    result = VisitInputExpression(e, inputVarName, type, out fromSymbol);
                    AddFromSymbol(result, inputVarName, fromSymbol);
                    symbolTable.ExitScope();
                    break;
            }

            if (addDefaultColumns && result.Select.IsEmpty)
            {
                var defaultColumns = AddDefaultColumns(result);
                if (markAllDefaultColumnsAsUsed)
                {
                    foreach (var symbol in defaultColumns)
                    {
                        optionalColumnUsageManager.MarkAsUsed(symbol);
                    }
                }
            }

            return result;
        }

        // <summary>
        // This method is called by <see cref="Visit(DbFilterExpression)" /> and
        // <see cref="Visit(DbQuantifierExpression)" />
        // </summary>
        // <param name="negatePredicate">
        // This is passed from <see cref="Visit(DbQuantifierExpression)" /> in the All(...) case.
        // </param>
        private SqlSelectStatement VisitFilterExpression(DbExpressionBinding input, DbExpression predicate, bool negatePredicate)
        {
            Symbol fromSymbol;
            var result = VisitInputExpression(
                input.Expression,
                input.VariableName, input.VariableType, out fromSymbol);

            // Filter is compatible with OrderBy
            // but not with Project, another Filter or GroupBy
            if (!IsCompatible(result, DbExpressionKind.Filter))
            {
                result = CreateNewSelectStatement(result, input.VariableName, input.VariableType, out fromSymbol);
            }

            selectStatementStack.Push(result);
            symbolTable.EnterScope();

            AddFromSymbol(result, input.VariableName, fromSymbol);

            if (negatePredicate)
            {
                result.Where.Append("NOT (");
            }
            result.Where.Append(predicate.Accept(this));
            if (negatePredicate)
            {
                result.Where.Append(")");
            }

            symbolTable.ExitScope();
            selectStatementStack.Pop();

            return result;
        }

        // <summary>
        // If the sql fragment for an input expression is not a SqlSelect statement
        // or other acceptable form (e.g. an extent as a SqlBuilder), we need
        // to wrap it in a form acceptable in a FROM clause.  These are
        // primarily the
        // <list type="bullet">
        //     <item>The set operation expressions - union all, intersect, except</item>
        //     <item>TVFs, which are conceptually similar to tables</item>
        // </list>
        // </summary>
        private static void WrapNonQueryExtent(SqlSelectStatement result, ISqlFragment sqlFragment, DbExpressionKind expressionKind)
        {
            switch (expressionKind)
            {
                case DbExpressionKind.Function:
                    // TVF
                    result.From.Append(sqlFragment);
                    break;

                default:
                    result.From.Append(" (");
                    result.From.Append(sqlFragment);
                    result.From.Append(")");
                    break;
            }
        }

        private static string ByteArrayToBinaryString(Byte[] binaryArray)
        {
            var sb = new StringBuilder(binaryArray.Length * 2);
            for (var i = 0; i < binaryArray.Length; i++)
            {
                sb.Append(_hexDigits[(binaryArray[i] & 0xF0) >> 4]).Append(_hexDigits[binaryArray[i] & 0x0F]);
            }
            return sb.ToString();
        }

        // <summary>
        // Helper method for the Group By visitor
        // Returns true if at least one of the aggregates in the given list
        // has an argument that is not a <see cref="DbConstantExpression" /> and is not
        // a <see cref="DbPropertyExpression" /> over <see cref="DbVariableReferenceExpression" />,
        // either potentially capped with a <see cref="DbCastExpression" />
        // This is really due to the following two limitations of Sql Server:
        // <list type="number">
        //     <item>
        //         If an expression being aggregated contains an outer reference, then that outer
        //         reference must be the only column referenced in the expression (SQLBUDT #488741)
        //     </item>
        //     <item>
        //         Sql Server cannot perform an aggregate function on an expression containing
        //         an aggregate or a subquery. (SQLBUDT #504600)
        //     </item>
        // </list>
        // Potentially, we could furhter optimize this.
        // </summary>
        private static bool GroupByAggregatesNeedInnerQuery(IList<DbAggregate> aggregates, string inputVarRefName)
        {
            foreach (var aggregate in aggregates)
            {
                Debug.Assert(aggregate.Arguments.Count == 1);
                if (GroupByAggregateNeedsInnerQuery(aggregate.Arguments[0], inputVarRefName))
                {
                    return true;
                }
            }
            return false;
        }

        // <summary>
        // Returns true if the given expression is not a <see cref="DbConstantExpression" /> or a
        // <see cref="DbPropertyExpression" /> over  a <see cref="DbVariableReferenceExpression" />
        // referencing the given inputVarRefName, either
        // potentially capped with a <see cref="DbCastExpression" />.
        // </summary>
        private static bool GroupByAggregateNeedsInnerQuery(DbExpression expression, string inputVarRefName)
        {
            return GroupByExpressionNeedsInnerQuery(expression, inputVarRefName, true);
        }

        // <summary>
        // Helper method for the Group By visitor
        // Returns true if at least one of the expressions in the given list
        // is not <see cref="DbPropertyExpression" /> over <see cref="DbVariableReferenceExpression" />
        // referencing the given inputVarRefName potentially capped with a <see cref="DbCastExpression" />.
        // This is really due to the following limitation: Sql Server requires each GROUP BY expression
        // (key) to contain at least one column that is not an outer reference. (SQLBUDT #616523)
        // Potentially, we could further optimize this.
        // </summary>
        private static bool GroupByKeysNeedInnerQuery(IList<DbExpression> keys, string inputVarRefName)
        {
            foreach (var key in keys)
            {
                if (GroupByKeyNeedsInnerQuery(key, inputVarRefName))
                {
                    return true;
                }
            }
            return false;
        }

        // <summary>
        // Returns true if the given expression is not <see cref="DbPropertyExpression" /> over
        // <see cref="DbVariableReferenceExpression" /> referencing the given inputVarRefName
        // potentially capped with a <see cref="DbCastExpression" />.
        // This is really due to the following limitation: Sql Server requires each GROUP BY expression
        // (key) to contain at least one column that is not an outer reference. (SQLBUDT #616523)
        // Potentially, we could further optimize this.
        // </summary>
        private static bool GroupByKeyNeedsInnerQuery(DbExpression expression, string inputVarRefName)
        {
            return GroupByExpressionNeedsInnerQuery(expression, inputVarRefName, false);
        }

        // <summary>
        // Helper method for processing Group By keys and aggregates.
        // Returns true if the given expression is not a <see cref="DbConstantExpression" />
        // (and allowConstants is specified)or a <see cref="DbPropertyExpression" /> over
        // a <see cref="DbVariableReferenceExpression" /> referencing the given inputVarRefName,
        // either potentially capped with a <see cref="DbCastExpression" />.
        // </summary>
        private static bool GroupByExpressionNeedsInnerQuery(DbExpression expression, string inputVarRefName, bool allowConstants)
        {
            //Skip a constant if constants are allowed
            if (allowConstants && (expression.ExpressionKind == DbExpressionKind.Constant))
            {
                return false;
            }

            //Skip a cast expression
            if (expression.ExpressionKind
                == DbExpressionKind.Cast)
            {
                var castExpression = (DbCastExpression)expression;
                return GroupByExpressionNeedsInnerQuery(castExpression.Argument, inputVarRefName, allowConstants);
            }

            //Allow Property(Property(...)), needed when the input is a join
            if (expression.ExpressionKind
                == DbExpressionKind.Property)
            {
                var propertyExpression = (DbPropertyExpression)expression;
                return GroupByExpressionNeedsInnerQuery(propertyExpression.Instance, inputVarRefName, allowConstants);
            }

            if (expression.ExpressionKind
                == DbExpressionKind.VariableReference)
            {
                var varRefExpression = expression as DbVariableReferenceExpression;
                return !varRefExpression.VariableName.Equals(inputVarRefName);
            }

            return true;
        }

        // <summary>
        // Throws not supported exception if the server is pre-katmai
        // </summary>
        private void AssertKatmaiOrNewer(PrimitiveTypeKind primitiveTypeKind)
        {
            AssertKatmaiOrNewer(_sqlVersion, primitiveTypeKind);
        }

        private static void AssertKatmaiOrNewer(SqlVersion sqlVersion, PrimitiveTypeKind primitiveTypeKind)
        {
            if (SqlVersionUtils.IsPreKatmai(sqlVersion))
            {
                throw new NotSupportedException(Strings.SqlGen_PrimitiveTypeNotSupportedPriorSql10(primitiveTypeKind));
            }
        }

        // <summary>
        // Throws not supported exception if the server is pre-katmai
        // </summary>
        internal void AssertKatmaiOrNewer(DbFunctionExpression e)
        {
            if (IsPreKatmai)
            {
                throw new NotSupportedException(Strings.SqlGen_CanonicalFunctionNotSupportedPriorSql10(e.Function.Name));
            }
        }
    }
}
