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https://issues.apache.org/jira/browse/CALCITE-4333?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17248094#comment-17248094
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Julian Hyde commented on CALCITE-4333:
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[~rubenql], I don't think it's possible to decorrelate your query. Your query
requires that we find out whether an employee is in the top 3 of their
department. After decorrelation, it returns the top 3 employee employees across
all departments, which is not the same thing.
My comment in CALCITE-1317,
{quote}We might benefit from a generalized Sort(limit) operator that can find
the top N within any prefix of the sort key, not just the top N overall.
{quote}
applies here also.
Can you please create a new JIRA case, and let's discuss there. I don't want to
undermine confidence in this fix, because I think it is good - in the limited
cases where it can be applied, it is applied, and produces valid queries.
> The Sort rel should be decorrelated even though it has fetch or limit when
> its parent is not a Correlate
> --------------------------------------------------------------------------------------------------------
>
> Key: CALCITE-4333
> URL: https://issues.apache.org/jira/browse/CALCITE-4333
> Project: Calcite
> Issue Type: Bug
> Components: core
> Affects Versions: 1.26.0
> Reporter: Danny Chen
> Assignee: Danny Chen
> Priority: Major
> Labels: pull-request-available
> Fix For: 1.27.0
>
> Time Spent: 1h 10m
> Remaining Estimate: 0h
>
> Check this test in SqlToRelConverterTest:
> {code:java}
> @Test void testSortLimitWithCorrelateInput() {
> final String sql = "" +
> "SELECT deptno, ename\n" +
> " FROM\n" +
> " (SELECT DISTINCT deptno FROM emp) t1,\n" +
> " LATERAL (\n" +
> " SELECT ename, sal\n" +
> " FROM emp\n" +
> " WHERE deptno = t1.deptno)\n" +
> " ORDER BY ename DESC\n" +
> " LIMIT 3";
> sql(sql).ok();
> }
> {code}
> The current plan is:
> {code:xml}
> LogicalSort(sort0=[$1], dir0=[DESC], fetch=[3])
> LogicalProject(DEPTNO=[$0], ENAME=[$1])
> LogicalCorrelate(correlation=[$cor0], joinType=[inner],
> requiredColumns=[{0}])
> LogicalAggregate(group=[{0}])
> LogicalProject(DEPTNO=[$7])
> LogicalTableScan(table=[[CATALOG, SALES, EMP]])
> LogicalProject(ENAME=[$1], SAL=[$5])
> LogicalFilter(condition=[=($7, $cor0.DEPTNO)])
> LogicalTableScan(table=[[CATALOG, SALES, EMP]])
> {code}
> It actually can be decorrelated to:
> {code:xml}
> LogicalSort(sort0=[$1], dir0=[DESC], fetch=[3])
> LogicalProject(DEPTNO=[$0], ENAME=[$1])
> LogicalJoin(condition=[=($0, $3)], joinType=[inner])
> LogicalAggregate(group=[{0}])
> LogicalProject(DEPTNO=[$7])
> LogicalTableScan(table=[[CATALOG, SALES, EMP]])
> LogicalProject(ENAME=[$1], SAL=[$5], DEPTNO=[$7])
> LogicalTableScan(table=[[CATALOG, SALES, EMP]])
> {code}
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