SupportsProjectionPushDown (Flink : Table : Common 2.0-preview1 API)

```
@PublicEvolving
public interface SupportsProjectionPushDown
```
Enables to push down a (possibly nested) projection into a ScanTableSource.
Given the following SQL:
```
 CREATE TABLE t (i INT, r ROW < d DOUBLE, b BOOLEAN>, s STRING);
 SELECT s, r.d FROM t;
 
```
In the above example, r.d and s are required fields. Other fields can be skipped in a projection. Compared to table's schema, fields are reordered.
By default, if this interface is not implemented, a projection is applied in a subsequent operation after the source.
For efficiency, a source can push a projection further down in order to be close to the actual data generation. A projection is only selecting fields that are used by a query (possibly in a different field order). It does not contain any computation. A projection can either be performed on the fields of the top-level row only or consider nested fields as well (see supportsNestedProjection()).
See Also:

Projection, ProjectedRowData

Method Summary

All Methods Instance Methods Abstract Methods Default Methods Deprecated Methods
Modifier and Type	Method	Description
`default void`	`applyProjection(int[][] projectedFields)`	Deprecated. Please implement `applyProjection(int[][], DataType)`
`default void`	`applyProjection(int[][] projectedFields, DataType producedDataType)`	Provides the field index paths that should be used for a projection.
`boolean`	`supportsNestedProjection()`	Returns whether this source supports nested projection.

- Method Detail
  - supportsNestedProjection
```
boolean supportsNestedProjection()
```
    Returns whether this source supports nested projection.
  - applyProjection
```
@Deprecated
default void applyProjection(int[][] projectedFields)
```
    Deprecated.
    Please implement applyProjection(int[][], DataType)
  - applyProjection
```
default void applyProjection(int[][] projectedFields,
                             DataType producedDataType)
```
    Provides the field index paths that should be used for a projection. The indices are 0-based and support fields within (possibly nested) structures if this is enabled via supportsNestedProjection().
    In the example mentioned in SupportsProjectionPushDown, this method would receive:
    
    [[2], [1]] which is equivalent to [["s"], ["r"]] if supportsNestedProjection() returns false.
    [[2], [1, 0]] which is equivalent to [["s"], ["r", "d"]]] if supportsNestedProjection() returns true.
    
    Note: Use the passed data type instead of ResolvedSchema.toPhysicalRowDataType() for describing the final output data type when creating TypeInformation.
    Parameters:
    
    projectedFields - field index paths of all fields that must be present in the physically produced data
    
    producedDataType - the final output type of the source, with the projection applied