Package org.apache.flink.table.connector.source.abilities

Interface SupportsProjectionPushDown

@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

Modifier and Type	Method	Description
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 Details

supportsNestedProjection

boolean supportsNestedProjection()

Returns whether this source supports nested projection.

applyProjection

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