UnionEliminatorRule (Apache Calcite API)

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

```
public class UnionEliminatorRule
extends RelOptRule
```
UnionEliminatorRule checks to see if its possible to optimize a Union call by eliminating the Union operator altogether in the case the call consists of only one input.

- Field Summary
  
  Fields
  Modifier and Type Field Description
  
  static UnionEliminatorRule INSTANCE
  - Fields inherited from class org.apache.calcite.plan.RelOptRule
    description, operands, relBuilderFactory
- Constructor Summary
  
  Constructors
  Constructor Description
  
  UnionEliminatorRule(java.lang.Class<? extends Union> clazz, RelBuilderFactory relBuilderFactory)
  Creates a UnionEliminatorRule.
- 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 UnionEliminatorRule INSTANCE
```
- Constructor Detail
  - UnionEliminatorRule
```
public UnionEliminatorRule(java.lang.Class<? extends Union> clazz,
                           RelBuilderFactory relBuilderFactory)
```
    Creates a UnionEliminatorRule.
- 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)