Hello,
I think that conditional indexes not so clever as can.. Just little one
example:
isbs=# create unique index person_login on person (login) where
login<>'';
CREATE INDEX
isbs=# explain select * from person where login='user';
QUERY PLAN
---------------------------------------------------------
Seq Scan on person (cost=0.00..53.34 rows=1 width=167)
Why it does not use person_login index - predicate login='user' definitely
also mean (login<>'') - indexes' predicate!
isbs=# explain select * from person where login='user' and login<>'';
QUERY PLAN
-----------------------------------------------------------------------------
Index Scan using person_login on person (cost=0.00..5.97 rows=1
width=167)
Postgres start to use conditional index only when I also pass index'
condition:
login='user' AND login<>'' ...
isbs=# select version();
version
---------------------------------------------------------------------
PostgreSQL 7.3.3 on i386-unknown-freebsd4.7, compiled by GCC 2.95.4
--
best regards,
Ruslan A Dautkhanov rusland@scn.ru