AggregateValuesRule (Apache Calcite API)

java.lang.Object
- org.apache.calcite.plan.RelOptRule
- - org.apache.calcite.rel.rules.AggregateValuesRule

```
public class AggregateValuesRule
extends RelOptRule
```
Rule that applies Aggregate to a Values (currently just an empty Values).
This is still useful because PruneEmptyRules.AGGREGATE_INSTANCE doesn't handle Aggregate, which is in turn because Aggregate of empty relations need some special handling: a single row will be generated, where each column's value depends on the specific aggregate calls (e.g. COUNT is 0, SUM is NULL).
Sample query where this matters:
SELECT COUNT(*) FROM s.foo WHERE 1 = 0

This rule only applies to "grand totals", that is, GROUP BY (). Any non-empty GROUP BY clause will return one row per group key value, and each group will consist of at least one row.

- Field Summary
  
  Fields
  Modifier and Type Field Description
  
  static AggregateValuesRule INSTANCE
  - Fields inherited from class org.apache.calcite.plan.RelOptRule
    description, operands, relBuilderFactory
- Constructor Summary
  
  Constructors
  Constructor Description
  
  AggregateValuesRule(RelBuilderFactory relBuilderFactory)
  Creates an AggregateValuesRule.
- Method Summary
  
  All Methods Instance Methods Concrete Methods
  Modifier and Type Method Description
  
  void onMatch(RelOptRuleCall call)
  Receives notification about a rule match.
  - Methods inherited from class org.apache.calcite.plan.RelOptRule
    any, convert, convert, convertList, convertOperand, convertOperand, equals, equals, getOperand, getOperands, getOutConvention, getOutTrait, hashCode, matches, none, operand, operand, operand, operand, operand, operandJ, operandJ, some, toString, unordered
  - Methods inherited from class java.lang.Object
    clone, finalize, getClass, notify, notifyAll, wait, wait, wait

- Field Detail
  - INSTANCE
```
public static final AggregateValuesRule INSTANCE
```
- Constructor Detail
  - AggregateValuesRule
```
public AggregateValuesRule(RelBuilderFactory relBuilderFactory)
```
    Creates an AggregateValuesRule.
    
    Parameters:
    
    relBuilderFactory - Builder for relational expressions
- Method Detail
  - onMatch
```
public void onMatch(RelOptRuleCall call)
```
    Description copied from class: RelOptRule
    
    Receives notification about a rule match. At the time that this method is called, call.rels holds the set of relational expressions which match the operands to the rule; call.rels[0] is the root expression.
    Typically a rule would check that the nodes are valid matches, creates a new expression, then calls back RelOptRuleCall.transformTo(org.apache.calcite.rel.RelNode, java.util.Map<org.apache.calcite.rel.RelNode, org.apache.calcite.rel.RelNode>) to register the expression.
    
    Specified by:
    
    onMatch in class RelOptRule
    
    Parameters:
    
    call - Rule call
    
    See Also:
    
    RelOptRule.matches(RelOptRuleCall)