Sean Hsuan-Yi Chu created CALCITE-844:
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Summary: The lack of Project under LogicalWindow hurts the
performance
Key: CALCITE-844
URL: https://issues.apache.org/jira/browse/CALCITE-844
Project: Calcite
Issue Type: Bug
Reporter: Sean Hsuan-Yi Chu
Assignee: Sean Hsuan-Yi Chu
Firstly of all, this issue happens when HepPlanner is used with
ProjectToWindowRule.PROJECT rule.
A simple query like:
{code}
select sum(deptno) over(partition by deptno) as sum1
from emp
{code}
produces
{code}
LogicalProject($0=[$9])
LogicalWindow(window#0=[window(partition {7} order by [] range between
UNBOUNDED PRECEDING and UNBOUNDED FOLLOWING aggs [SUM($7)])])
LogicalTableScan(table=[[CATALOG, SALES, EMP]])
{code}
However, from performance standpoint, it is better to have a project between
LogicalWindow and LogicalTableScan since only one column is used.
Interestingly, when there is an expression in the window function. For example,
{code}
select sum(deptno + 1) over(partition by deptno) as sum1
from emp"
{code}
produces
{code}
LogicalProject($0=[$2])
LogicalWindow(window#0=[window(partition {0} order by [] range between
UNBOUNDED PRECEDING and UNBOUNDED FOLLOWING aggs [SUM($1)])])
LogicalProject(DEPTNO=[$7], $1=[+($7, 1)])
LogicalTableScan(table=[[CATALOG, SALES, EMP]])
{code}
The LogicalProject below window can trim out useless columns or even be pushed
into Scan, which is very important optimization Calcite can exploit.
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