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https://issues.apache.org/jira/browse/CALCITE-2936?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16798331#comment-16798331
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Julian Hyde commented on CALCITE-2936:
--------------------------------------
Yeah, I agree it's a bit weird to use metaData during sql-to-rel conversion.
However, I think it's OK (especially as MinRowCount is "safe", not an
estimate). We already use it when {{SqlToRelConverter}} calls
{{RelBuilder.aggregate}}.
It's a long shot, but is there any way to push this logic into
{{RelBuilder.semiJoin}}? Then people would get it whether they use
SqlToRelConverter or some other means (say within a rule).
> Simplify EXISTS or NOT EXISTS sub-query that has "GROUP BY ()"
> --------------------------------------------------------------
>
> Key: CALCITE-2936
> URL: https://issues.apache.org/jira/browse/CALCITE-2936
> Project: Calcite
> Issue Type: New Feature
> Reporter: Haisheng Yuan
> Priority: Major
> Labels: pull-request-available
> Time Spent: 1h 10m
> Remaining Estimate: 0h
>
> An EXISTS or NOT EXISTS sub-query whose inner child is an aggregate with no
> grouping columns should be simplified to a Boolean constant.
> Example:
> {code:java}
> exists(select sum(i) from X) --> true
> not exists(select sum(i) from X) --> false
> {code}
> Repro:
> {code:java}
> @Test public void testExistentialSubquery() {
> final String sql = "SELECT e1.empno\n"
> + "FROM emp e1 where exists\n"
> + "(select avg(sal) from emp e2 where e1.empno = e2.empno )";
> sql(sql).decorrelate(true).ok();
> }
> {code}
> We got plan:
> {code:java}
> LogicalProject(EMPNO=[$0])
> LogicalProject(EMPNO=[$0], ENAME=[$1], JOB=[$2], MGR=[$3], HIREDATE=[$4],
> SAL=[$5], COMM=[$6], DEPTNO=[$7], SLACKER=[$8], EMPNO0=[CAST($9):INTEGER],
> $f1=[CAST($10):BOOLEAN])
> LogicalJoin(condition=[=($0, $9)], joinType=[inner])
> LogicalTableScan(table=[[CATALOG, SALES, EMP]])
> LogicalAggregate(group=[{0}], agg#0=[MIN($1)])
> LogicalProject(EMPNO=[$0], $f0=[true])
> LogicalAggregate(group=[{0}], EXPR$0=[AVG($1)])
> LogicalProject(EMPNO=[$0], SAL=[$5])
> LogicalTableScan(table=[[CATALOG, SALES, EMP]])
> {code}
> The preferred plan should be:
> {code:java}
> LogicalProject(EMPNO=[$0])
> LogicalTableScan(table=[[CATALOG, SALES, EMP]])
> {code}
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