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https://issues.apache.org/jira/browse/CALCITE-4437?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17250746#comment-17250746
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Danny Chen commented on CALCITE-4437:
-------------------------------------
Would take a look if i found some time ~
> The Sort rel should be decorrelated even though it has fetch or limit when it
> is not inside a Correlate
> -------------------------------------------------------------------------------------------------------
>
> Key: CALCITE-4437
> URL: https://issues.apache.org/jira/browse/CALCITE-4437
> Project: Calcite
> Issue Type: Bug
> Components: core
> Affects Versions: 1.26.0
> Reporter: Ruben Q L
> Priority: Major
> Labels: pull-request-available
> Fix For: 1.27.0
>
> Time Spent: 10m
> Remaining Estimate: 0h
>
> The fix applied for CALCITE-4206 was "too drastic" and it resulted in Sort
> with fetch/offset being impossible to decorrelate in all cases.
> CALCITE-4333 addressed this issue but only partially (when the Sort with
> fetch/offset is on top on the plan). However, this solution is insufficient,
> because any Sort with fetch/offset that is not inside a Correlate can be
> decorrelated.
> Check this test in SqlToRelConverterTest (same test as CALCITE-4333, just
> with an extra LogicalProject on top of the LogicalSort):
> {code}
> @Test void testProjectSortLimitWithCorrelateInput() {
> final String sql = ""
> + "SELECT ename||deptno FROM\n"
> + " (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:
> {noformat}
> LogicalProject(EXPR$0=[||($1, CAST($0):VARCHAR NOT NULL)])
> 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]])
> {noformat}
> It can actually decorrelated as:
> {noformat}
> LogicalProject(EXPR$0=[||($1, CAST($0):VARCHAR NOT NULL)])
> 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]])
> {noformat}
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