[CALCITE-3015] Add rule to remove constants in group keys

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Duplicate
• Fix Version/s: 1.20.0
• Assignee: Chunwei Lei
• Reporter: Chunwei Lei
• Created: 22/Apr/19 13:09
• Updated: 24/Jun/19 21:51
• Resolved: 23/Apr/19 11:01

Description

Constants in group keys can be removed to reduce shuffle. For instance, 

 

select key, value, count(*) from (select 1 as key, value from src) dual group by key, value;

can be reduced to

select value, count(*) from (select 1 as key, value from src) dual group by value;

It could save much resource in distribute system if all group keys are constants since the distribution becomes SINGLETON instead of HASH.

Issue Links

• duplicates: CALCITE-1023 Planner rule that removes Aggregate keys that are constant