com.facebook.presto.spi

Interface ColumnHandle

public interface ColumnHandle

Method Summary

Modifier and Type	Method and Description
default ColumnHandle	withRequiredSubfields(List<Subfield> subfields) Applies to columns of complex types: arrays, maps and structs.

Method Detail

withRequiredSubfields

@Experimental
default ColumnHandle withRequiredSubfields(List<Subfield> subfields)

Applies to columns of complex types: arrays, maps and structs. When a query uses only some of the subfields, the engine provides the complete list of required subfields and the connector is free to prune the rest.

Examples: - SELECT a[1], b['x'], x.y.z FROM t - SELECT a FROM t WHERE b['y'] > 10

Pruning must preserve the type of the values and support unmodified access.

- Pruning a struct means populating some of the members with null values. - Pruning a map means dropping keys not listed in the required subfields. - Pruning arrays means dropping values with indices larger than maximum required index and filling in remaining non-required indices with nulls.