Re: OR clause causing strange index performance

Hi!

I read your JOIN - Index Scaning - OR problem. I don't understand why
you decomposed JOINs two brach (ul1 and ul2).
If I understand your problem well I can suggest the next idea for your
QUERY (you don't need two branch):

SELECT * FROM permissions p
INNER JOIN users u ON u.id = p.id
INNER JOIN user_list ul ON ul.id = u.id
INNER JOIN lists l ON ( l.list_id1 = ul.list_id1 AND
l.list_id2 = ul.list_id2 )
WHERE
(ul.type = '1' OR ul.type= '2') and p.code = '123456' AND p.type =
'User';

If ul.type field is integer you can optimze the OR (which can cause
index scan problem and low performance) with BETWEEN:

SELECT * FROM permissions p
INNER JOIN users u ON u.id = p.id
INNER JOIN user_list ul ON ul.id = u.id
INNER JOIN lists l ON ( l.list_id1 = ul.list_id1 AND
l.list_id2 = ul.list_id2 )
WHERE
ul.type BETWEEN 1 AND 2 and p.code = '123456' AND p.type = 'User';

After that you need some good index on ul.type, p.code and p.type. You
have to think about creating indices. Analyse the results of explain!!!
In my opinion this solution may be very fast.

Regards,
Antal Attila

-----Original Message-----
From: pgsql-sql-owner(at)postgresql(dot)org
[mailto:pgsql-sql-owner(at)postgresql(dot)org] On Behalf Of Doug Y
Sent: Thursday, May 20, 2004 7:32 PM
To: pgsql-sql(at)postgresql(dot)org
Subject: [SQL] OR clause causing strange index performance

SELECT *
FROM permissions p
INNER JOIN users u
ON u.id = p.id
LEFT JOIN user_list ul1
ON ul1.id = u.id
AND ul1.type = '1'
LEFT JOIN user_list ul2
ON ul2.id = u.id
AND ul2.type = '2'
INNER JOIN lists l
ON ( l.list_id1 = ul1.list_id1 AND l.list_id2 =
ul1.list_id2 )
OR
( l.list_id1 = ul2.list_id1 AND l.list_id2 =
ul2.list_id2 )
WHERE
p.code = '123456' AND p.type = 'User'