Cannot use MySQL user variables after INTO clause #854

Describe the bug
Using MySQL user variables after the INTO clause in a SELECT is a perfectly valid MySQL query. But the parse is unable to parse such a query.

To Reproduce
Steps to reproduce the behavior:

1. Example SQL:

   SELECT COUNT(*) INTO @countTotal FROM employee;

2. Parsing this SQL using JSqlParser with this statements:

       try {
           Statement userVariableAfterInto =
                   CCJSqlParserUtil.parse("SELECT COUNT(*) INTO @countTotal FROM employee;");
       } catch (JSQLParserException e) {
           e.printStackTrace();
       }

3. Exception

   Caused by: net.sf.jsqlparser.parser.ParseException: Encountered unexpected token: "@" "@"
       at line 1, column 22.
   
   Was expecting one of:
   
   	"ACTION"
       "ANY"
       "BYTE"
       "CASCADE"

Expected behavior
It should be possible to use MySQL user variables after the INTO clause of the SELECT query.

System

• Database you are using: MySQL
• Java Version: 11.0.3
• JSqlParser version: 3.0