[jira] [Created] (CALCITE-3763) RelBuilder.aggregate should prune unused fields from the input, if the input is a Project

["Julian Hyde (Jira)" <ji...@apache.org>]

Julian Hyde created CALCITE-3763:
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             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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