From: Nathan Young <nyoung@asis.com>
To: pgsql-sql@postgresql.org
Date: Wed, 27 Nov 2002 09:37:07 -0800
Reply-To: nathan@ncyoung.com
Organization: N.C. Young Design
In-Reply-To: <20021126080514.C77510-100000@megazone23.bigpanda.com>
Message-Id: <98FCPJ2YA0B9EDSOVU5ZURIFVR76US2X.3de502c3@inky>
Subject: Re: join question
MIME-Version: 1.0
Content-Type: text/plain; charset="US-ASCII"

OK, that works great, but I was told that I should avoid sub-selects when 
possible for performance reasons.  Also, I used so much mental energy trying 
to find a solution that would do either task using a join that I would be 
very curious if anyone had a solution.

The setup:
>> I have a table with members and a table with payments.  Each payment is
>> related to a member by memberID and each payment has (among other things)
>> a year paid.

The problem:

>> I would like to be able to get a list of members who have not paid for a
>> given year.

Two possible solutions, both using sub-selects:

> select member.memberId, member.name from member where not exists (select
>  * from payment where payment.memberId=member.memberID and
>  payment.yearPaid=2002);
>
> select member.memberId, member.name from member left outer join
>  (select * from payment where yearPaid=2002) as a using (memberId) where
>  yearPaid is null;

In addition to my interest in finding a join that could do that, I'm curios 
about a couple other things.

My understanding is that exists is optimized so that the first version would 
be faster than the second.

"using (memberID)" would be the same as "on member.memberID = 
payment.memberID", right?


Thanks!

------------->Nathan


11/26/2002 8:11:53 AM, Stephan Szabo <sszabo@megazone23.bigpanda.com> wrote:

>
>On Fri, 22 Nov 2002, Nathan Young wrote:
>
>> Hi all.
>>
>> I have a table with members and a table with payments.  Each payment is
>> related to a member by memberID and each payment has (among other things) 
a
>> year paid.
>>
>> I can create a join to find a list of members who have paid for a given 
year
>> (2002 in this case):
>>
>> select member.memberID,member.name from member, payment where
>> payment.memberID = member.memberID and payment.yearPaid = 2002
>>
>> I would like to be able to get a list of members who have not paid for a
>> given year.
>
>Well, I believe either of these two will do that:
>
> select member.memberId, member.name from member where not exists (select
>  * from payment where payment.memberId=member.memberID and
>  payment.yearPaid=2002);
>
> select member.memberId, member.name from member left outer join
>  (select * from payment where yearPaid=2002) as a using (memberId) where
>  yearPaid is null;
>
>> I would also like to combine the two criteria, for example to generate a 
list
>> of members who have paid for 2002 but not 2003.
>
>I think these would do that:
>
>select member.memberID,member.name from member, payment where
> payment.memberID = member.memberID and payment.yearPaid = 1999
> and not exists (select * from payment where
> payment.memberId=member.memberId and yearPaid=2002);
>
>select member.memberId, member.name from member inner join (select
> * from payment where yearPaid=2002) as a using (memberId) left outer join
> (select * from payment where yearPaid=2003) as b using (memberId) where
> b.yearPaid is null;
>
>
>
>


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Nathan Young
N. C. Young Design
(530)629-4176
http://ncyoung.com