This query surprised me. I expected us to do the Aggregate once for all the aggregate functions in the select target which is what normally happens. If I simplify the query further it actually does so.
I don't really understand what's going on here. It can't be the volatile random() because in fact even if I make them depend on the random value the subplans are executed with the same parameter values anyways and the sums end up being the same. postgres=# postgres=# explain select sum(n),sum(n) from (select (select count(*) as n from a ) as n from (select random() as s) as xyzzy) as xyzzy ; QUERY PLAN ----------------------------------------------------------------------- Aggregate (cost=5676.06..5676.07 rows=1 width=0) InitPlan -> Aggregate (cost=2838.00..2838.01 rows=1 width=0) -> Seq Scan on a (cost=0.00..2588.00 rows=100000 width=0) -> Aggregate (cost=2838.00..2838.01 rows=1 width=0) -> Seq Scan on a (cost=0.00..2588.00 rows=100000 width=0) -> Result (cost=0.00..0.01 rows=1 width=0) (7 rows) -- Gregory Stark EnterpriseDB http://www.enterprisedb.com Ask me about EnterpriseDB's On-Demand Production Tuning -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers