[CALCITE-3144] Add rule, AggregateCaseToFilterRule, that converts "SUM(CASE WHEN b THEN x END)" to "SUM(x) FILTER (WHERE b)"

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 1.21.0
• Assignee: Julian Hyde
• Reporter: Julian Hyde
• Created: 24/Jun/19 18:40
• Updated: 10/Sep/19 21:36
• Resolved: 15/Jul/19 17:57

Description

Add a rule that converts "SUM(CASE WHEN b THEN x END)" to "SUM(x) FILTER (WHERE b)".

Druid added CaseFilteredAggregatorRule in https://github.com/apache/incubator-druid/pull/4360.

Maybe AggregateCaseToFilterRule is a slightly better name. Or maybe this transform could be done in RelBuilder.aggregate, and we wouldn't need a rule.