Gautam Kumar Parai created DRILL-4771: -----------------------------------------
Summary: Drill should avoid doing the same join twice if count(distinct) exists Key: DRILL-4771 URL: https://issues.apache.org/jira/browse/DRILL-4771 Project: Apache Drill Issue Type: Improvement Affects Versions: 1.6.0 Reporter: Gautam Kumar Parai Assignee: Gautam Kumar Parai When the query has one distinct aggregate and one or more non-distinct aggregates, the join instance need not produce the join-based plan. We can generate multi-phase aggregates. Another approach would be to use grouping sets. However, Drill is unable to support grouping sets and instead relies on the join-based plan (see the plan below) {code} select emp.empno, count(*), avg(distinct dept.deptno) from sales.emp emp inner join sales.dept dept on emp.deptno = dept.deptno group by emp.empno LogicalProject(EMPNO=[$0], EXPR$1=[$1], EXPR$2=[$3]) LogicalJoin(condition=[IS NOT DISTINCT FROM($0, $2)], joinType=[inner]) LogicalAggregate(group=[{0}], EXPR$1=[COUNT()]) LogicalProject(EMPNO=[$0], DEPTNO0=[$9]) LogicalJoin(condition=[=($7, $9)], joinType=[inner]) LogicalTableScan(table=[[CATALOG, SALES, EMP]]) LogicalTableScan(table=[[CATALOG, SALES, DEPT]]) LogicalAggregate(group=[{0}], EXPR$2=[AVG($1)]) LogicalAggregate(group=[{0, 1}]) LogicalProject(EMPNO=[$0], DEPTNO0=[$9]) LogicalJoin(condition=[=($7, $9)], joinType=[inner]) LogicalTableScan(table=[[CATALOG, SALES, EMP]]) LogicalTableScan(table=[[CATALOG, SALES, DEPT]]) {code} The more efficient form should look like this {code} select emp.empno, count(*), avg(distinct dept.deptno) from sales.emp emp inner join sales.dept dept on emp.deptno = dept.deptno group by emp.empno LogicalAggregate(group=[{0}], EXPR$1=[SUM($2)], EXPR$2=[AVG($1)]) LogicalAggregate(group=[{0, 1}], EXPR$1=[COUNT()]) LogicalProject(EMPNO=[$0], DEPTNO0=[$9]) LogicalJoin(condition=[=($7, $9)], joinType=[inner]) LogicalTableScan(table=[[CATALOG, SALES, EMP]]) LogicalTableScan(table=[[CATALOG, SALES, DEPT]]) {code} -- This message was sent by Atlassian JIRA (v6.3.4#6332)