Vineet Garg created CALCITE-1495:
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Summary: 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
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