2010/8/17 Tom Lane <t...@sss.pgh.pa.us>: > =?ISO-8859-1?Q?C=E9dric_Villemain?= <cedric.villemain.deb...@gmail.com> > writes: >> Here we are. A simple usecase. > > The reason you have an issue here is that the column is char(n) while > the parameter is text. So the non-USING execute is equivalent to > > regression=# explain SELECT flag FROM foo where uid = > 'cfcd208495d565ef66e7dff9f98764da'; > QUERY PLAN > -------------------------------------------------------------------- > Index Scan using foo_pkey on foo (cost=0.00..8.27 rows=1 width=1) > Index Cond: (uid = 'cfcd208495d565ef66e7dff9f98764da'::bpchar) > (2 rows) > > while the EXECUTE USING is equivalent to > > regression=# explain SELECT flag FROM foo where uid = > 'cfcd208495d565ef66e7dff9f98764da'::text; > QUERY PLAN > -------------------------------------------------------------------- > Seq Scan on foo (cost=0.00..24.02 rows=5 width=1) > Filter: ((uid)::text = 'cfcd208495d565ef66e7dff9f98764da'::text) > (2 rows) > > and the reason you don't get an indexscan on the latter is that it's a > TEXT comparison not a BPCHAR comparison; which is different because of > the rules about ignoring trailing blanks. > > char(n) sucks. Avoid it if possible. If you insist on using it, > be very very careful about which comparison semantics you're asking for.
Oh! Thank you very much for those clarifications. ... and I am sorry for the noisy report ... -- Cédric Villemain 2ndQuadrant http://2ndQuadrant.fr/ PostgreSQL : Expertise, Formation et Support -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
