BuiltInMetadata.RowCount (Apache Calcite API)

All Superinterfaces:

Metadata

All Known Subinterfaces:

BuiltInMetadata.All

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 MetadataDef<BuiltInMetadata.RowCount> DEF

Method Summary

All Methods Instance Methods Abstract Methods
Modifier and Type	Method	Description
`java.lang.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 Detail
  - DEF
```
static final MetadataDef<BuiltInMetadata.RowCount> DEF
```
- Method Detail
  - getRowCount
```
java.lang.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