net.sf.farrago.query
Class FarragoReduceExpressionsRule

java.lang.Object
  org.eigenbase.relopt.RelOptRule
      net.sf.farrago.query.FarragoReduceExpressionsRule

public abstract class FarragoReduceExpressionsRule
extends RelOptRule

Collection of planner rules that apply various simplifying transformations on RexNode trees. Currently, there are two transformations:

• Constant reduction, which evaluates constant subtrees, replacing them with a corresponding RexLiteral
• Removal of redundant casts, which occurs when the argument into the cast is the same as the type of the resulting cast expression

Version:

$Id: //open/dev/farrago/src/net/sf/farrago/query/FarragoReduceExpressionsRule.java#27 $

Author:

John V. Sichi

Nested Class Summary

private static class	FarragoReduceExpressionsRule.ReducibleExprLocator Helper class used to locate expressions that either can be reduced to literals or contain redundant casts.
(package private) static class	FarragoReduceExpressionsRule.ReentrantValuesStmt Evaluates constant expressions via a reentrant query of the form "VALUES (exp1, exp2, exp3, ...)".
private static class	FarragoReduceExpressionsRule.RexReplacer Replaces expressions with their reductions.

Field Summary

static FarragoReduceExpressionsRule	calcInstance
static Pattern	EXCLUSION_PATTERN Regular expression which matches the description of all instances of this rule and FarragoReduceValuesRule also.
static FarragoReduceExpressionsRule	filterInstance Singleton rule which reduces constants inside a FilterRel.
static FarragoReduceExpressionsRule	joinInstance
static FarragoReduceExpressionsRule	projectInstance

Fields inherited from class org.eigenbase.relopt.RelOptRule

ANY, description, operands

Constructor Summary

private

FarragoReduceExpressionsRule(Class<? extends RelNode> relClass) Creates a new FarragoReduceExpressionsRule object.

Method Summary

private static void	findReducibleExps(FarragoSessionPreparingStmt preparingStmt, List<RexNode> exps, List<RexNode> constExps, List<Boolean> addCasts, List<RexNode> removableCasts) Locates expressions that can be reduced to literals or converted to expressions with redundant casts removed.
(package private) static FarragoSession	getSession(RelNode rel)
(package private) static boolean	reduceExpressions(RelNode rel, List<RexNode> expList) Reduces a list of expressions.

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

EXCLUSION_PATTERN

public static final Pattern EXCLUSION_PATTERN

Regular expression which matches the description of all instances of this rule and FarragoReduceValuesRule also. Use it to prevent the planner from invoking these rules.

filterInstance

public static final FarragoReduceExpressionsRule filterInstance

Singleton rule which reduces constants inside a FilterRel. If the condition is a constant, the filter is removed (if TRUE) or replaced with EmptyRel (if FALSE or NULL).

projectInstance

public static final FarragoReduceExpressionsRule projectInstance

joinInstance

public static final FarragoReduceExpressionsRule joinInstance

calcInstance

public static final FarragoReduceExpressionsRule calcInstance

Constructor Detail

FarragoReduceExpressionsRule

private FarragoReduceExpressionsRule(Class<? extends RelNode> relClass)

Creates a new FarragoReduceExpressionsRule object.

Parameters:

relClass - class of rels to which this rule should apply

Method Detail

reduceExpressions

static boolean reduceExpressions(RelNode rel,
                                 List<RexNode> expList)

Reduces a list of expressions.

Parameters:

rel - Relational expression

expList - List of expressions, modified in place

Returns:

whether reduction found something to change, and succeeded

getSession

static FarragoSession getSession(RelNode rel)

findReducibleExps

private static void findReducibleExps(FarragoSessionPreparingStmt preparingStmt,
                                      List<RexNode> exps,
                                      List<RexNode> constExps,
                                      List<Boolean> addCasts,
                                      List<RexNode> removableCasts)

Locates expressions that can be reduced to literals or converted to expressions with redundant casts removed.

Parameters:

preparingStmt - the statement containing the expressions

exps - list of candidate expressions to be examined for reduction

constExps - returns the list of expressions that can be constant reduced

addCasts - indicator for each expression that can be constant reduced, whether a cast of the resulting reduced expression is potentially necessary

removableCasts - returns the list of cast expressions where the cast can be removed