On Thu, Mar 16, 2017 at 4:45 AM, Andres Freund <and...@anarazel.de> wrote: > During citus development we noticed that restrictions aren't pushed down > into lateral subqueries, even if they semantically could. For example, > in this dumbed down example: > > postgres[31776][1]=# CREATE TABLE t_2(id serial primary key); > postgres[31776][1]=# CREATE TABLE t_1(id serial primary key); > > Comparing: > > postgres[31776][1]=# EXPLAIN SELECT * FROM t_1 JOIN (SELECT * FROM t_2 GROUP > BY id) s ON (t_1.id = s.id) WHERE t_1.id = 3; > postgres[31776][1]=# EXPLAIN SELECT * FROM t_1, LATERAL (SELECT * FROM t_2 > WHERE t_1.id = t_2.id GROUP BY id) s WHERE t_1.id = 3;
Interesting. That does seem like we are missing a trick. Not exactly related, but I think we need to improve optimization around CTEs, too. AFAICT, what we've got right now, almost everybody hates. -- Robert Haas EnterpriseDB: http://www.enterprisedb.com The Enterprise PostgreSQL Company -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
