## UPDATE

To start an UPDATE query, use one of the `update` methods in [QueryBuilderDsl]. There are several
variants depending on whether your table name is qualified, and whether you use case-sensitive
identifiers or case-insensitive strings:

```java
import static com.datastax.oss.driver.api.querybuilder.QueryBuilderDsl.*;

UpdateStart update = update("user");
```

Note that, at this stage, the query can't be built yet. You need at least one
[assignment](#assignments) and one [relation](#relations).

### Timestamp

The USING TIMESTAMP clause comes right after the table, and specifies the timestamp at which the
mutation will be applied. You can pass either a literal value:

```java
update("user").usingTimestamp(1234);
// UPDATE user USING TIMESTAMP 1234...
```

Or a bind marker:

```java
update("user").usingTimestamp(bindMarker());
// UPDATE user USING TIMESTAMP ?...
```

If you call the method multiple times, the last value will be used.

### Assignments

An assignment is an operation that appears after the SET keyword. You need at least one for a valid
update query.

The easiest way to add an assignment is with one of the fluent methods:

```java
update("user").setColumn("v", bindMarker());
// UPDATE user SET v=?...
```

You can also create it manually with one of the factory methods in [Assignment], and then pass it to
`set()`:

```java
update("user").set(
    Assignment.setColumn("v", bindMarker()));
// UPDATE user SET v=?...
```

If you have multiple assignments, you can add them all in a single call. This is a bit more
efficient since it creates less temporary objects:

```java
update("user").set(
    Assignment.setColumn("v1", bindMarker()),
    Assignment.setColumn("v2", bindMarker()))
// UPDATE user SET v1=?,v2=?...
```

#### Simple columns

As shown already, `setColumn` changes the value of a column. It can take a bind marker or a literal
(which must have the same CQL type as the column):

```java
update("user").setColumn("last_name", literal("Doe"));
// UPDATE user SET last_name='Doe'...
```

#### UDT fields

`setField` modifies a field inside of a UDT column:

```java
update("user").setField("address", "street", bindMarker());
// UPDATE user SET address.street=?...
```

#### Counters

Counter columns can be incremented by a given amount:

```java
update("foo").increment("c", bindMarker());
// UPDATE foo SET c+=?...

update("foo").increment("c", literal(4));
// UPDATE foo SET c+=4...
```

There is a shortcut to increment by 1:

```java
update("foo").increment("c");
// UPDATE foo SET c+=1...
```

All those methods have a `decrement` counterpart:

```java
update("foo").decrement("c");
// UPDATE foo SET c-=1...
```

#### Collections

`mapValue` changes a value in a map. The key is expressed as a term (here a literal value) :

```java
update("product").setMapValue("features", literal("color"), bindMarker())
// UPDATE product SET features['color']=?...
```

`append` operates on any CQL collection type (list, set or map). If you pass a literal, it must also
be a collection, with the same CQL type of elements:

```java
update("foo").append("l", bindMarker());
// UPDATE foo SET l+=?...

List<Integer> value = Arrays.asList(1, 2, 3);
update("foo").append("l", literal(value));
// UPDATE foo SET l+=[1,2,3]...

Set<Integer> value = new HashSet<>(Arrays.asList(1, 2, 3));
update("foo").append("s", literal(value))
// UPDATE foo SET s+={1,2,3}...

Map<Integer, String> value = new HashMap<>();
value.put(1, "bar");
value.put(2, "baz");
update("foo").append("m", literal(value));
// UPDATE foo SET m+={1:'bar',2:'baz'}...
```

If you only have one element to append, there are shortcuts to avoid creating a collection in your
code:

```java
update("foo").appendListElement("l", literal(1));
// UPDATE foo SET l+=[1]...

update("foo").appendSetElement("s", literal(1));
// UPDATE foo SET s+={1}...

update("foo").appendMapEntry("m", literal(1), literal("bar"));
// UPDATE foo SET m+={1:'bar'}...
```

All those methods have a `prepend` counterpart:

```java
update("foo").prepend("l", bindMarker());
// UPDATE foo SET l=?+l...
```

As well as a `remove` counterpart:

```java
update("foo").remove("l", bindMarker());
// UPDATE foo SET l-=?...
```

### Relations

Once you have at least one assignment, relations can be added with the fluent `whereXxx()` methods:

```java
update("foo").setColumn("v", bindMarker()).whereColumn("k").isEqualTo(bindMarker());
// UPDATE foo SET v=? WHERE k=?
```

Or you can build and add them manually:

```java
update("foo").setColumn("v", bindMarker()).where(
    Relation.column("k").isEqualTo(bindMarker()));
// UPDATE foo SET v=? WHERE k=?
```

Once there is at least one assignment and one relation, the statement can be built:

```java
SimpleStatement statement = update("foo")
    .setColumn("k", bindMarker())
    .whereColumn("k").isEqualTo(bindMarker())
    .build();
```

Relations are a common feature used by many types of statements, so they have a
[dedicated page](../relation) in this manual.

### Conditions

Conditions get added with the fluent `ifXxx()` methods:

```java
update("foo")
    .setColumn("v", bindMarker())
    .whereColumn("k").isEqualTo(bindMarker())
    .ifColumn("v").isEqualTo(bindMarker());
// UPDATE foo SET v=? WHERE k=? IF v=?
```

Or you can build and add them manually:

```java
update("foo")
    .setColumn("v", bindMarker())
    .whereColumn("k").isEqualTo(bindMarker())
    .if_(
        Condition.column("v").isEqualTo(bindMarker()));
// UPDATE foo SET v=? WHERE k=? IF v=?
```

Conditions are a common feature used by UPDATE and DELETE, so they have a
[dedicated page](../condition) in this manual.

[QueryBuilderDsl]: http://docs.datastax.com/en/drivers/java/4.0/com/datastax/oss/driver/api/query-builder/QueryBuilderDsl.html
[Assignment]:      http://docs.datastax.com/en/drivers/java/4.0/com/datastax/oss/driver/api/query-builder/update/Assignment.html
