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1147035203
A WHERE clause applied to the output of a subquery with DISTINCT should theoretically be applied only once per distinct row; but if we push it into the subquery then it will be evaluated at each row before duplicate elimination occurs. If the qual is volatile this can give rise to observably wrong results, so don't do that. While at it, refactor a little bit to allow subquery_is_pushdown_safe to report more than one kind of restrictive condition without indefinitely expanding its argument list. Although this is a bug fix, it seems unwise to back-patch it into released branches, since it might de-optimize plans for queries that aren't giving any trouble in practice. So apply to 9.4 but not further back. |
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