BuiltInMetadata.ColumnUniqueness (Apache Calcite API)

All Superinterfaces:

Metadata

All Known Subinterfaces:

BuiltInMetadata.All

Enclosing class:

BuiltInMetadata
```
public static interface BuiltInMetadata.ColumnUniqueness
extends Metadata
```
Metadata about whether a set of columns uniquely identifies a row.

Nested Class Summary

Nested Classes
Modifier and Type Interface Description

static interface BuiltInMetadata.ColumnUniqueness.Handler
Handler API.

Field Summary

Fields
Modifier and Type Field Description

static MetadataDef<BuiltInMetadata.ColumnUniqueness> DEF

Method Summary

All Methods Instance Methods Abstract Methods
Modifier and Type	Method	Description
`java.lang.Boolean`	`areColumnsUnique(ImmutableBitSet columns, boolean ignoreNulls)`	Determines whether a specified set of columns from a specified relational expression are unique.

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

- Field Detail
  - DEF
```
static final MetadataDef<BuiltInMetadata.ColumnUniqueness> DEF
```
- Method Detail
  - areColumnsUnique
```
java.lang.Boolean areColumnsUnique(ImmutableBitSet columns,
                                   boolean ignoreNulls)
```
    Determines whether a specified set of columns from a specified relational expression are unique.
    For example, if the relational expression is a TableScan to T(A, B, C, D) whose key is (A, B), then:
    
    areColumnsUnique([0, 1]) yields true,
    areColumnsUnique([0]) yields false,
    areColumnsUnique([0, 2]) yields false.
    
    Nulls can be ignored if the relational expression has filtered out null values.
    Parameters:
    
    columns - column mask representing the subset of columns for which uniqueness will be determined
    
    ignoreNulls - if true, ignore null values when determining column uniqueness
    
    Returns:
    
    whether the columns are unique, or null if not enough information is available to make that determination