SupportsTargetColumnWriting (Flink : Table : Common 2.1.0 API)

```
@PublicEvolving
public interface SupportsTargetColumnWriting
```
Interface for DynamicTableSinks that support target column writing.
The planner will parse target columns from the DML clause and call applyTargetColumns(int[][]) to pass an array of column index paths to the sink.
The array indices are 0-based and support composite columns within (possibly nested) structures. This information comes from the column list of the DML clause, e.g., for a sink table t1 whose schema is: a STRING, b ROW < b1 INT, b2 STRING>, c BIGINT
- insert: 'insert into t1(a, b.b2) ...', the column list will be 'a, b.b2', and will provide [[0], [1, 1]]. The statement 'insert into t1 select ...' will provide an empty list and will not apply this ability.
- update: 'update t1 set a=1, b.b1=2 where ...', the column list will be 'a, b.b1', and will provide [[0], [1, 0]].
Note: Planner will not apply this ability for the delete statement because it has no column list.
A sink can use this information to perform target columns writing.
If this interface is implemented and applyTargetColumns(int[][]) returns true. The planner will use this information for plan optimization such as sink reuse.

Method Summary

All Methods Instance Methods Abstract Methods
Modifier and Type	Method	Description
`boolean`	`applyTargetColumns(int[][] targetColumns)`	Provides an array of column index paths related to user specified target column list.

- Method Detail
  - applyTargetColumns
```
boolean applyTargetColumns(int[][] targetColumns)
```
    Provides an array of column index paths related to user specified target column list.
    See the documentation of SupportsTargetColumnWriting for more information.
    
    Parameters:
    
    targetColumns - column index paths
    
    Returns:
    
    true if the target columns are applied successfully, false otherwise.