Re: Is a better way to have the same result of this

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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