[jira] [Resolved] (CALCITE-4560) Wrong plan when decorrelating EXISTS subquery with COALESCE in the predicate

["Stamatis Zampetakis (Jira)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/CALCITE-4560?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Stamatis Zampetakis resolved CALCITE-4560.
------------------------------------------
      Assignee: Stamatis Zampetakis
    Resolution: Fixed

Fixed in [d7b3c83e06e4a63e5cb97c6f93b66795556d53db|https://github.com/apache/calcite/commit/d7b3c83e06e4a63e5cb97c6f93b66795556d53db]. Thanks for the reviews [~jamesstarr], [~julianhyde]!

> Wrong plan when decorrelating EXISTS subquery with COALESCE in the predicate
> ----------------------------------------------------------------------------
>
>                 Key: CALCITE-4560
>                 URL: https://issues.apache.org/jira/browse/CALCITE-4560
>             Project: Calcite
>          Issue Type: Bug
>          Components: core
>    Affects Versions: 1.26.0
>            Reporter: Stamatis Zampetakis
>            Assignee: Stamatis Zampetakis
>            Priority: Major
>              Labels: pull-request-available
>             Fix For: 1.27.0
>
>          Time Spent: 1.5h
>  Remaining Estimate: 0h
>
> The problem can be seen by adding the following test in {{SqlToRelConverterTest}}.
> {code:java}
>   @Test void testExistsCorrelatedDecorrelate01() {
>     final String sql = "select e1.empno from empnullables e1 where exists (\n"
>         + "  select 1 from empnullables e2 where COALESCE(e1.ename,'M')=COALESCE(e2.ename,'M'))";
>     sql(sql).decorrelate(true).ok();
>   }
> {code}
> The plan after decorrelation is shown below:
> {noformat}
> LogicalProject(EMPNO=[$0])
>   LogicalProject(EMPNO=[$0], ENAME=[$1], JOB=[$2], MGR=[$3], HIREDATE=[$4], SAL=[$5], COMM=[$6], DEPTNO=[$7], SLACKER=[$8], ENAME0=[$9], $f1=[CAST($10):BOOLEAN])
>     LogicalJoin(condition=[=($1, $9)], joinType=[inner])
>       LogicalTableScan(table=[[CATALOG, SALES, EMPNULLABLES]])
>       LogicalAggregate(group=[{0}], agg#0=[MIN($1)])
>         LogicalProject(ENAME0=[$9], $f0=[true])
>           LogicalJoin(condition=[=(CASE(IS NOT NULL($9), $9, 'M':VARCHAR(20)), CASE(IS NOT NULL($1), CAST($1):VARCHAR(20) NOT NULL, 'M':VARCHAR(20)))], joinType=[inner])
>             LogicalTableScan(table=[[CATALOG, SALES, EMPNULLABLES]])
>             LogicalAggregate(group=[{0}])
>               LogicalProject(ENAME=[$1])
>                 LogicalTableScan(table=[[CATALOG, SALES, EMPNULLABLES]])
> {noformat}
> The problem lies in the {{LogicalJoin(condition=[=($1, $9)], joinType=[inner])}} operator. If there are rows with {{NULL}} values in the {{ENAME}} column these are going to be incorrectly removed from the result set. The COALESCE operator is present in the SQL query to ensure that rows with NULL values are retained in the result.



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