[CALCITE-6201] Merge Aggregate node if count distinct column has been deduplicated

• Type: Improvement
• Status: Resolved
• Priority: Minor
• Resolution: Duplicate
• Fix Version/s: 1.37.0
• Component/s: core
• Assignee: Jiajun Xie
• Reporter: Jiajun Xie
• Created: 14/Jan/24 07:17
• Updated: 22/Apr/24 14:25
• Resolved: 21/Jan/24 08:02

Description

distinct column is redundant because count has distinct. 

select count(distinct x) cnt
from(
   select distinct sal x from emp
) t 

PlanBefore is

LogicalAggregate(group=[{}], CNT=[COUNT(DISTINCT $0)])
  LogicalAggregate(group=[{5}])
    LogicalTableScan(table=[[CATALOG, SALES, EMP]])

PlanAfter should be 

LogicalAggregate(group=[{}], CNT=[COUNT(DISTINCT $5)])
    LogicalTableScan(table=[[CATALOG, SALES, EMP]])

But `CoreRules.AGGREGATE_MERGE` not support it, we can improve it.

 

Issue Links

• is duplicated by: CALCITE-6214 Remove DISTINCT in aggregate function if field is unique