Package org.apache.calcite.rel.metadata

Interface BuiltInMetadata.RowCount

All Superinterfaces:

Metadata

Enclosing class:

BuiltInMetadata

public static interface BuiltInMetadata.RowCount
extends Metadata

Metadata about the number of rows returned by a relational expression.

Nested Class Summary

Nested Classes

Modifier and Type	Interface	Description
static interface	BuiltInMetadata.RowCount.Handler	Handler API.

Field Summary

Fields

Modifier and Type	Field	Description
static final MetadataDef<BuiltInMetadata.RowCount>	DEF

Method Summary

Modifier and Type	Method	Description
@Nullable Double	getRowCount()	Estimates the number of rows which will be returned by a relational expression.

Methods inherited from interface org.apache.calcite.rel.metadata.Metadata

rel

Field Details

DEF

static final MetadataDef<BuiltInMetadata.RowCount> DEF

Method Details

getRowCount

@Nullable Double getRowCount()

Estimates the number of rows which will be returned by a relational expression. The default implementation for this query asks the rel itself via RelNode.estimateRowCount(org.apache.calcite.rel.metadata.RelMetadataQuery), but metadata providers can override this with their own cost models.

Returns:

estimated row count, or null if no reliable estimate can be determined