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Vineet Garg commented on CALCITE-1495: -------------------------------------- Thanks Julian. I did not know that Calcite already has a SemiJoinRule. Does this Rule already takes your point #1 (none of the columns on the RHS are being used) into consideration or does the caller need to make sure of that ? {Quote} Can you give an example of an optimization that this rule makes possible? {Quote} The reason I suggested this rule is because HIVE supports LEFT SEMI JOIN natively. Doing LEFT SEMI JOIN only instead of doing GROUP BY + INNER JOIN should be more efficient in this case. I am not aware of any logical optimization this rule makes possible. > Add a rule to convert INNER JOIN preceded by GROUP BY to appropriate SEMI-JOIN > ------------------------------------------------------------------------------ > > Key: CALCITE-1495 > URL: https://issues.apache.org/jira/browse/CALCITE-1495 > Project: Calcite > Issue Type: New Feature > Components: core > Reporter: Vineet Garg > Assignee: Julian Hyde > > For IN and EXISTS subqueries Calcite currently generates plan consisting of > GROUP BY on inner table followed by INNER JOIN with outer table. > e.g. for following query: > {noformat} select sal from emp where empno IN (select deptno from dept) > {noformat} > Generated plan is: > {noformat} > LogicalProject(SAL=[$5]) > LogicalProject(EMPNO=[$0], ENAME=[$1], JOB=[$2], MGR=[$3], HIREDATE=[$4], > SAL=[$5], COMM=[$6], DEPTNO=[$7], SLACKER=[$8]) > LogicalJoin(condition=[=($0, $9)], joinType=[inner]) > LogicalTableScan(table=[[CATALOG, SALES, EMP]]) > LogicalAggregate(group=[{0}]) > LogicalProject(DEPTNO=[$0]) > LogicalTableScan(table=[[CATALOG, SALES, DEPT]]) > {noformat} > Such cases could be converted using this rule to use SEMI-JOIN to make it > more efficient -- This message was sent by Atlassian JIRA (v6.3.4#6332)