On Thu, Dec 14, 2017 at 4:01 PM, Ashutosh Bapat <ashutosh.ba...@enterprisedb.com> wrote: > + > +-- Test when input relation for grouping is dummy > +EXPLAIN (COSTS OFF) > +SELECT c, sum(a) FROM pagg_tab WHERE 1 = 2 GROUP BY c; > + QUERY PLAN > +-------------------------------- > + HashAggregate > + Group Key: pagg_tab.c > + -> Result > + One-Time Filter: false > +(4 rows) > > Not part of your patch, I am wondering if we can further optimize this plan by > converting HashAggregate to Result (One-time Filter: false) and the aggregate > target. Just an idea. > This comment is also wrong. The finalization step of aggregates needs to be executed irrespective of whether or not the underlying scan produces any rows. It may, for example, add a constant value to the transition result. We may apply this optimization only when none of aggregations have finalization functions, but it may not be worth the code.
-- Best Wishes, Ashutosh Bapat EnterpriseDB Corporation The Postgres Database Company
