2010/1/12 Matteo Beccati <p...@beccati.com>: > Il 12/01/2010 08:55, Pavel Stehule ha scritto: >> >> I checked query and I was surprised with very strange plan: >> >> postgres=# explain select a, b from a,b,c; >> QUERY PLAN >> ----------------------------------------------------------------------- >> Nested Loop (cost=0.00..276595350.00 rows=13824000000 width=8) >> -> Nested Loop (cost=0.00..115292.00 rows=5760000 width=8) >> -> Seq Scan on a (cost=0.00..34.00 rows=2400 width=4) >> -> Materialize (cost=0.00..82.00 rows=2400 width=4) >> -> Seq Scan on b (cost=0.00..34.00 rows=2400 width=4) >> -> Materialize (cost=0.00..82.00 rows=2400 width=0) >> -> Seq Scan on c (cost=0.00..34.00 rows=2400 width=0) >> (7 rows) > > It doesn't surprise me. Tables are empty, thus get a default non-0 row > estimate, which happens to be 2400: >
I though so default estimate is used only when table wasn't analysed. But you have a true. I am verifying it on 8.3 and the behave is same. so all is ok. Regards Pavel Stehule > test=# create table a (a int); > CREATE TABLE > test=# ANALYZE a; > ANALYZE > test=# EXPLAIN SELECT * from a; > QUERY PLAN > ----------------------------------------------------- > Seq Scan on a (cost=0.00..14.80 rows=2400 width=4) > (1 row) > > > That said, 2400^3 (cross join of 3 tables) == 13824000000 > > > Cheers > -- > Matteo Beccati > > Development & Consulting - http://www.beccati.com/ > -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
