org.apache.calcite.rel.rules

Class AggregateReduceFunctionsRule

java.lang.Object

org.apache.calcite.plan.RelOptRule

org.apache.calcite.rel.rules.AggregateReduceFunctionsRule

public class AggregateReduceFunctionsRule
extends RelOptRule

Planner rule that reduces aggregate functions in Aggregates to simpler forms.

Rewrites:

• AVG(x) → SUM(x) / COUNT(x)
• STDDEV_POP(x) → SQRT( (SUM(x * x) - SUM(x) * SUM(x) / COUNT(x)) / COUNT(x))
• STDDEV_SAMP(x) → SQRT( (SUM(x * x) - SUM(x) * SUM(x) / COUNT(x)) / CASE COUNT(x) WHEN 1 THEN NULL ELSE COUNT(x) - 1 END)
• VAR_POP(x) → (SUM(x * x) - SUM(x) * SUM(x) / COUNT(x)) / COUNT(x)
• VAR_SAMP(x) → (SUM(x * x) - SUM(x) * SUM(x) / COUNT(x)) / CASE COUNT(x) WHEN 1 THEN NULL ELSE COUNT(x) - 1 END

Since many of these rewrites introduce multiple occurrences of simpler forms like COUNT(x), the rule gathers common sub-expressions as it goes.

Field Summary

Fields

Modifier and Type	Field and Description
static AggregateReduceFunctionsRule	INSTANCE The singleton.

Fields inherited from class org.apache.calcite.plan.RelOptRule

description, operands

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	AggregateReduceFunctionsRule(RelOptRuleOperand operand)

Method Summary

Methods

Modifier and Type	Method and Description
boolean	matches(RelOptRuleCall call) Returns whether this rule could possibly match the given operands.
protected Aggregate	newAggregateRel(Aggregate oldAggregate, RelNode input, List<AggregateCall> newCalls) Do a shallow clone of oldAggRel and update aggCalls.
void	onMatch(RelOptRuleCall ruleCall) Receives notification about a rule match.

Methods inherited from class org.apache.calcite.plan.RelOptRule

any, convert, convert, convertList, equals, equals, getOperand, getOperands, getOutConvention, getOutTrait, hashCode, none, operand, operand, operand, operand, operand, some, toString, unordered

Methods inherited from class java.lang.Object

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

Field Detail

INSTANCE

public static final AggregateReduceFunctionsRule INSTANCE

The singleton.

Constructor Detail

AggregateReduceFunctionsRule

protected AggregateReduceFunctionsRule(RelOptRuleOperand operand)

Method Detail

matches

public boolean matches(RelOptRuleCall call)

Description copied from class: RelOptRule

Returns whether this rule could possibly match the given operands.

This method is an opportunity to apply side-conditions to a rule. The RelOptPlanner calls this method after matching all operands of the rule, and before calling RelOptRule.onMatch(RelOptRuleCall).

In implementations of RelOptPlanner which may queue up a matched RelOptRuleCall for a long time before calling RelOptRule.onMatch(RelOptRuleCall), this method is beneficial because it allows the planner to discard rules earlier in the process.

The default implementation of this method returns true. It is acceptable for any implementation of this method to give a false positives, that is, to say that the rule matches the operands but have RelOptRule.onMatch(RelOptRuleCall) subsequently not generate any successors.

The following script is useful to identify rules which commonly produce no successors. You should override this method for these rules:

awk '
 /Apply rule/ {rule=$4; ruleCount[rule]++;}
 /generated 0 successors/ {ruleMiss[rule]++;}
 END {
   printf "%-30s %s %s\n", "Rule", "Fire", "Miss";
   for (i in ruleCount) {
     printf "%-30s %5d %5d\n", i, ruleCount[i], ruleMiss[i];
   }
 } ' FarragoTrace.log

Overrides:

matches in class RelOptRule

Parameters:

call - Rule call which has been determined to match all operands of this rule

Returns:

whether this RelOptRule matches a given RelOptRuleCall

onMatch

public void onMatch(RelOptRuleCall ruleCall)

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:

ruleCall - Rule call

See Also:

RelOptRule.matches(RelOptRuleCall)

newAggregateRel

protected Aggregate newAggregateRel(Aggregate oldAggregate,
                        RelNode input,
                        List<AggregateCall> newCalls)

Do a shallow clone of oldAggRel and update aggCalls. Could be refactored into Aggregate and subclasses - but it's only needed for some subclasses.

Parameters:

oldAggregate - LogicalAggregate to clone.

input - Input relational expression

newCalls - New list of AggregateCalls

Returns:

shallow clone with new list of AggregateCalls.