org.eigenbase.rel.rules
Class RemoveEmptyRule

java.lang.Object
  org.eigenbase.relopt.RelOptRule
      org.eigenbase.rel.rules.RemoveEmptyRule

public abstract class RemoveEmptyRule
extends RelOptRule

Collection of rules which remove sections of a query plan known never to produce any rows.

Version:

$Id: //open/dev/farrago/src/org/eigenbase/rel/rules/RemoveEmptyRule.java#7 $

Author:

Julian Hyde

See Also:

EmptyRel

Field Summary

static RemoveEmptyRule	filterInstance Singleton instance of rule which converts a FilterRel to empty if its child is empty.
static RemoveEmptyRule	projectInstance Singleton instance of rule which converts a ProjectRel to empty if its child is empty.
static RemoveEmptyRule	unionInstance Singleton instance of rule which removes empty children of a UnionRel.

Fields inherited from class org.eigenbase.relopt.RelOptRule

ANY, description, operands

Constructor Summary

private

RemoveEmptyRule(RelOptRuleOperand operand, String desc) Creates a RemoveEmptyRule.

Method Summary

Methods inherited from class org.eigenbase.relopt.RelOptRule

convert, equals, equals, getOperand, getOperands, getOutConvention, getOutTrait, hashCode, matches, mergeTraitsAndConvert, mergeTraitsAndConvert, onMatch, toString

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Field Detail

unionInstance

public static final RemoveEmptyRule unionInstance

Singleton instance of rule which removes empty children of a UnionRel.

Examples:

• Union(Rel, Empty, Rel2) becomes Union(Rel, Rel2)
• Union(Rel, Empty, Empty) becomes Rel
• Union(Empty, Empty) becomes Empty

projectInstance

public static final RemoveEmptyRule projectInstance

Singleton instance of rule which converts a ProjectRel to empty if its child is empty.

Examples:

• Project(Empty) becomes Empty

filterInstance

public static final RemoveEmptyRule filterInstance

Singleton instance of rule which converts a FilterRel to empty if its child is empty.

Examples:

• Filter(Empty) becomes Empty

Constructor Detail

RemoveEmptyRule

private RemoveEmptyRule(RelOptRuleOperand operand,
                        String desc)

Creates a RemoveEmptyRule.

Parameters:

operand - Operand

desc - Description