Maryann Xue created CALCITE-938:
-----------------------------------
Summary: Make Aggregate return more accurate rowCount if groupSet
is unique keys.
Key: CALCITE-938
URL: https://issues.apache.org/jira/browse/CALCITE-938
Project: Calcite
Issue Type: Improvement
Reporter: Maryann Xue
Assignee: Maryann Xue
Priority: Minor
If columns in "select distinct" are already distinct, there can be two sets of
equivalent rel before and after AggregateRemoveRule.
{code}
agg
| input
input
10.0 100.0
{code}
Based on the default implementation of rel metadata, the rowCount of the
"before" rel is only 1/10 of that of the "after" rel, but meanwhile the "after"
rel is definitely cheaper. So the Volcano planner would most likely either fail
to pick the cheapest one or have an inconsistent state due to CALCITE-830.
An example (based EnumerableRel cost model):
The plan for
{code}
select empno, d.deptno
from "scott".emp
join (select distinct deptno from "scott".dept) d
using (deptno);
{code}
would be
{code}
EnumerableCalc(expr#0..2=[{inputs}], EMPNO=[$t1], DEPTNO=[$t0])
EnumerableJoin(condition=[=($0, $2)], joinType=[inner])
EnumerableAggregate(group=[$0])
EnumerableTableScan(table=[[scott, DEPT]])
EnumerableCalc(expr#0..7=[{inputs}], EMPNO=[$t0], DEPTNO=[$t7])
EnumerableTableScan(table=[[scott, EMP]])
{code}
, while it should be
{code}
EnumerableCalc(expr#0..2=[{inputs}], EMPNO=[$t1], DEPTNO=[$t0])
EnumerableJoin(condition=[=($0, $2)], joinType=[inner])
EnumerableCalc(expr#0..2=[{inputs}], DEPTNO=[$t0])
EnumerableTableScan(table=[[scott, DEPT]])
EnumerableCalc(expr#0..7=[{inputs}], EMPNO=[$t0], DEPTNO=[$t7])
EnumerableTableScan(table=[[scott, EMP]])
{code}
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