Package org.apache.calcite.rel.metadata
Interface MetadataFactory
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- 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
.
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Method Summary
All Methods Instance Methods Abstract Methods Modifier and Type Method Description <M extends Metadata>
Mquery(RelNode rel, RelMetadataQuery mq, java.lang.Class<M> metadataClazz)
Returns a metadata interface to get a particular kind of metadata from a particular relational expression.
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Method Detail
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query
<M extends Metadata> M query(RelNode rel, RelMetadataQuery mq, java.lang.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 expressionmq
- Metadata querymetadataClazz
- Metadata class- Returns:
- Metadata bound to
rel
andquery
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