org.apache.calcite.rel.metadata

Interface MetadataFactory

All Known Implementing Classes:

MetadataFactoryImpl

public interface MetadataFactory

Source of metadata about relational expressions.

The metadata is typically various kinds of statistics used to estimate costs.

Each kind of metadata has an interface that extends Metadata and has a method. Some examples: BuiltInMetadata.Selectivity, BuiltInMetadata.ColumnUniqueness.

Method Summary

Modifier and Type	Method and Description
<M extends Metadata> M	query(RelNode rel, RelMetadataQuery mq, Class<M> metadataClazz) Returns a metadata interface to get a particular kind of metadata from a particular relational expression.

Method Detail

query

<M extends Metadata> M query(RelNode rel,
                             RelMetadataQuery mq,
                             Class<M> metadataClazz)

Returns a metadata interface to get a particular kind of metadata from a particular relational expression. Returns null if that kind of metadata is not available.

Type Parameters:

M - Metadata type

Parameters:

rel - Relational expression

mq - Metadata query

metadataClazz - Metadata class

Returns:

Metadata bound to rel and query