From: Jie Liang <jie@stbernard.com>
To: Dmitry Tkach <dmitry@openratings.com>
To: pgsql-general@postgresql.org
To: pgsql-sql@postgresql.org
Subject: Re: [SQL] Please, HELP! Why is the query plan so wrong???
Date: Thu, 11 Jul 2002 16:26:43 -0700
Message-ID: <7C760DAA511DC74B99E7D22189F786F101BF211C@MAIL01.stbernard.com> (raw)
I believe that SQL will use the index of join 'key' when you join the tables
if
have any, in your query the (a,c) is the join key but d is not.
Jie Liang
-----Original Message-----
From: Dmitry Tkach [mailto:dmitry@openratings.com]
Sent: Thursday, July 11, 2002 3:51 PM
To: pgsql-general@postgresql.org; pgsql-sql@postgresql.org
Subject: [SQL] Please, HELP! Why is the query plan so wrong???
Hi, everybody!
Here is the problem:
test=# create table fb (a int, b int, c datetime);
CREATE
test=# create table fbr (a int, c datetime, d int);
CREATE
test=# create unique index fb_idx on fb(b);
CREATE
test=# create index fbr_idx on fbr(a,c) where d is null;
CREATE
test=# set enable_seqscan=off;
SET VARIABLE
rapidb=# explain select * from fb, fbr where fb.b=0 and fb.a=fbr.a and
fb.c=fbr.c and fbr.d is null;
NOTICE: QUERY PLAN:
Hash Join (cost=100000005.82..100001015.87 rows=1 width=32)
-> Seq Scan on fbr (cost=100000000.00..100001010.00 rows=5 width=16)
-> Hash (cost=5.81..5.81 rows=1 width=16)
-> Index Scan using fb_idx on fb (cost=0.00..5.81 rows=1
width=16)
Could someone PLEASE explain to me, why doesn't it want to use the index on
fbr?
If I get rid of the join, then it works:
test=# explain select * from fbr where a=1 and c=now() and d is null;
NOTICE: QUERY PLAN:
Index Scan using fbr_idx on fbr (cost=0.00..5.82 rows=1 width=16)
What's the catch???
Any help would be greatly appreciated!
Thanks!
Dima
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To: pgsql-sql@postgresql.org
Cc: jie@stbernard.com, dmitry@openratings.com, pgsql-general@postgresql.org
Subject: Re: [SQL] Please, HELP! Why is the query plan so wrong???
In-Reply-To: <7C760DAA511DC74B99E7D22189F786F101BF211C@MAIL01.stbernard.com>
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