I guess my first message was not accurate, since t1 is a view, that includes t2.
Attached are the real queries with their corresponding plans, the first one takes 10.8 sec to execute, the second one takes 0.6 sec.
To simplify, I expanded the view, so the attached query refers to tables only.
Martijn van Oosterhout wrote:
Please supply EXPLAIN ANALYZE output.
On Sun, Oct 26, 2003 at 12:25:37AM +0300, Yonatan Goraly wrote:
I am in the process of adding PostgreSQL support for an application, in
addition to Oracle and MS SQL.
I am using PostgreSQL version 7.3.2, Red Hat 9.0 on Intel Pentium III board.
I have a query that generally looks like this:
SELECT t1.col1, t2.col1 FROM t1, t2 WHERE t1.x=t2.y AND t2.p='string'
AND t2.q=1
This query is strikingly slow (about 100 sec when both t1 and t2 has
about 1,200 records, compare with less than 4 sec with MS SQL and Oracle)
The strange thing is that if I remove one of the last 2 conditions
(doesn't matter which one), I get the same performance like with the
other databases.
Since in this particular case both conditions ( t2.p='string', t2.q=1)
are not required, I can't understand why having both turns the query so
slow.
A query on table t2 alone is fast with or without the 2 conditions.
I tired several alternatives, this one works pretty well:
SELECT t1.col1, t2.col1 FROM t1, t2 WHERE t1.x=t2.y AND EXISTS ( SELECT * FROM t2 t2a WHERE t2a.p='string' AND t2a.q=1 AND
t2a.y=t2.y )
Since the first query is simpler than the second, it seems to me like a bug.
Please advise
Yonatan