saffron.rel
Class SwapJoinRule

java.lang.Object
  |
  +--saffron.opt.Rule
        |
        +--saffron.rel.SwapJoinRule

public class SwapJoinRule

extends Rule

SwapJoinRule permutes the inputs to a join. Outer joins cannot be permuted.

Field Summary

Fields inherited from class saffron.opt.Rule

description, planner

Constructor Summary

SwapJoinRule()

Method Summary

void	onMatch(RuleCall call) This method is called every time the rule matches.
static Project	swap(Join join) Returns a relational expression with the inputs switched round.

Methods inherited from class saffron.opt.Rule

convert, getOutConvention, toString

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

SwapJoinRule

public SwapJoinRule()

Method Detail

swap

public static Project swap(Join join)

Returns a relational expression with the inputs switched round. Does not modify join. Returns null if the join cannot be swapped (for example, because it is an outer join).

onMatch

public void onMatch(RuleCall call)

Description copied from class: Rule

This method is called every time the rule matches. 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 RuleCall.transformTo(saffron.rel.Rel) to register the expression.

Specified by:

onMatch in class Rule