public interface MetadataFactory
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
.
Modifier and Type | Method and Description |
---|---|
<M extends Metadata> |
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.
|
<M extends Metadata> M query(RelNode rel, RelMetadataQuery mq, java.lang.Class<M> metadataClazz)
M
- Metadata typerel
- Relational expressionmq
- Metadata querymetadataClazz
- Metadata classrel
and query
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