Julian Hyde created CALCITE-3763:
Summary: RelBuilder.aggregate should prune unused fields from the
input, if the input is a Project
Key: CALCITE-3763
URL: https://issues.apache.org/jira/browse/CALCITE-3763
Project: Calcite
Issue Type: Bug
Reporter: Julian Hyde
{{RelBuilder.aggregate}} should prune unused fields from the input, if the
input is a {{Project}}.
Pruning fields during the planning process is desirable, but often cannot do it
- we are applying a {{RelOptRule}} that has to return the same fields, or we
don't want to add an extra Project do so the pruning. But when we are in
{{RelBuilder.aggregate}} and the input is a Project, neither of those
limitations apply. We already have a Project, we are just making it narrower;
and we know what fields the {{Aggregate}} will produce.
For example,
{code:sql}
SELECT deptno, SUM(sal) FILTER (WHERE b)
FROM (
SELECT deptno, empno + 10, sal, job = 'CLERK' AS b
FROM emp)
GROUP BY deptno
{code}
becomes
{code:sql}
SELECT deptno, SUM(sal) FILTER (WHERE b)
FROM (
SELECT deptno, sal, job = 'CLERK' AS b
FROM emp)
GROUP BY deptno
{code}
If there are no fields used, remove the {{Project}}. (A {{RelNode}} with no
fields is not allowed.)
{code:sql}
SELECT COUNT(*) AS C
FROM (
SELECT deptno, empno + 10, sal, job = 'CLERK' AS b
FROM emp)
{code}
becomes
{code:sql}
SELECT COUNT(*) AS c
FROM emp
{code}
Add an option {{RelBuilder.Config.pruneInputOfAggregate}}, default true, so
that people can disable this rewrite if it causes problems.
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