I just learnt the "common knowledge" about four hourse ago. That does help to improve the performance indeed
according to the explain command.
12/5/2002 11:45:26 AM, Jean-Luc Lachance <jllachan@nsd.ca> wrote:
>It is now common knowledge that the IN clause should be rewriten as an
>EXISTS.
>
>SELECT p.userid, p.year, a.country, a.province, a.city
>FROM profile p, account a
>WHERE p.userid=a.userid AND
> (p.year BETWEEN 1961 AND 1976) AND
> a.country='CA' AND
> a.province='BC' AND
> p.gender='f' AND
> NOT EXISTS ( SELECT 1 FROM block b WHERE b.personid='Joe' AND p.userid
>= b.userid) AND
> block.userid IS NOT NULL AND
> EXISTS ( SELECT 1 FROM preference f, profile p1
> WHERE p1.userid='Joe' AND p.userid = f.userif AND
> 2002-p1.year BETWEEN f.minage AND f.maxage);
>
>
>
>Vernon Wu wrote:
>>
>> Ron,
>>
>> The gender is indexed. Each user has account and preference, but not necessary block.
>>
>> I am currently seeking for query optimisation, not system configuration optimisation
>>
>> 12/4/2002 9:26:48 PM, Ron Johnson <ron.l.johnson@cox.net> wrote:
>>
>> >On Wed, 2002-12-04 at 18:26, Vernon Wu wrote:
>> >> I have the following query:
>> >>
>> >> SELECT p.userid, p.year, a.country, a.province, a.city
>> >> FROM profile p, account a
>> >> WHERE p.userid=a.userid AND
>> >> (p.year BETWEEN 1961 AND 1976) AND
>> >> a.country='CA' AND
>> >> a.province='BC' AND
>> >> p.gender='f' AND
>> >> p.userid NOT IN (SELECT b.userid FROM block b WHERE b.personid='Joe') AND
>> >> block.userid IS NOT NULL AND
>> >> p.userid IN
>> >> (SELECT f.userid FROM preference f, profile p1 WHERE p1.userid='Joe' AND 2002-p1.year BETWEEN
>> >> f.minage AND f.maxage)
>> >>
>> >> In plain English, it is that
>> >>
>> >> Joe finds females between the ages in the location who is not in the block table, while Joe's age is between what
>> they
>> >> prefer.
>> >>
>> >> The query plan is the followings:
>> >>
>> >> Nested Loop (cost=0.00..127.12 rows=995 width=894)
>> >> -> Nested Loop (cost=0.00..97.17 rows=1 width=894)
>> >> -> Seq Scan on account a (cost=0.00..25.00 rows=1 width=289)
>> >> -> Index Scan using pk_profile on profile p (cost=0.00..72.16 rows=1 width=605)
>> >> SubPlan
>> >> -> Materialize (cost=22.50..22.50 rows=5 width=55)
>> >> -> Seq Scan on block b (cost=0.00..22.50 rows=5 width=55
>> >> )
>> >> -> Materialize (cost=44.82..44.82 rows=111 width=89)
>> >> -> Nested Loop (cost=0.00..44.82 rows=111 width=89)
>> >> -> Index Scan using pk_profile on profile p1 (cost=0.00..4.82 rows=1 width=12)
>> >> -> Seq Scan on preference f (cost=0.00..20.00 rows=1000 width=77)
>> >> -> Seq Scan on block (cost=0.00..20.00 rows=995 width=0)
>> >>
>
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