We sometimes transform IN-clauses to a list of ORs:
postgres=# explain SELECT * FROM foo WHERE a IN (b, c);
QUERY PLAN
------------------------------------------------------
Seq Scan on foo (cost=0.00..39.10 rows=19 width=12)
Filter: ((a = b) OR (a = c))
(2 rows)
But what if you replace "a" with a volatile function? It doesn't seem
legal to do that transformation in that case, but we do it:
postgres=# explain SELECT * FROM foo WHERE (random()*2)::integer IN (b, c);
QUERY PLAN
-------------------------------------------------------------------------------------------------
-------------------
Seq Scan on foo (cost=0.00..68.20 rows=19 width=12)
Filter: ((((random() * 2::double precision))::integer = b) OR
(((random() * 2::double precision))::integer = c))
(2 rows)
I tried to read the SQL spec to see if it has anything to say about
that, but I couldn't find anything. My common sense says that that
transformation is not legal.
--
Heikki Linnakangas
EnterpriseDB http://www.enterprisedb.com
--
Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-hackers
