[jira] [Comment Edited] (CALCITE-4437) The Sort rel should be decorrelated even though it has fetch or limit when it is not inside a Correlate

["Thomas Rebele (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CALCITE-4437?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17248935#comment-17248935 ] 

Thomas Rebele edited comment on CALCITE-4437 at 12/14/20, 12:02 PM:
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A workaround for the issue: add a parameter isCorVarDefined to the decorrelateRel(...) methods, e.g., decorrelateRel(Sort rel, boolean isCorVarDefined). The parameter is true if the rel is inside of the right child of a decorrelate. At least this solves the case for us.

Edit: we may not decorrelate sorts in a right subtree of a correlate, even if it does not contain a correlate variable. CALCITE-4206 is an example for that case.


was (Author: thomas.rebele):
A workaround for the issue: add a parameter isCorVarDefined to the decorrelateRel(...) methods, e.g., decorrelateRel(Sort rel, boolean isCorVarDefined). The parameter is true if the rel is inside of the right child of a decorrelate. At least this solves the case for us.

It does not decorrelate sorts that are in a right subtree of a correlate, but do not have the correlation variable. It might be possible to decorrelate those too, but I haven't thought about it yet. Any counterexamples are welcome.

> 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
>             Fix For: 1.27.0
>
>
> 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 testSortLimitWithCorrelateInput2() {
>     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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