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Date: Fri, 07 Feb 2003 15:38:59 +0100
From: Tomasz Myrta <jasiek@klaster.net>
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To: Gary Stainburn <gary.stainburn@ringways.co.uk>
Cc: pgsql-sql@postgresql.org
Subject: Re: efficient count/join query
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Gary Stainburn wrote:
> On Friday 07 Feb 2003 1:26 pm, Tomasz Myrta wrote:
> 
>>Gary Stainburn wrote:
>>
 
<cut>
> 
> Many appologoes Tomasz.
No problem
> 
> Because your select *LOOKED* wrong to me, I didn't even try it.  Upon looking 
> at it again I can see what you're doing.  When I tried, it complained about 
> the counts and grouping, so I moved the count(*) to a sub-select and changed 
> the coalesce and it's working.
There were 2 bugs in this query:
- in group by - add field hcount
- counting when any roster doesn't exist for some history. Here is (I suppose) final query:

create view some_view as
select
 coalesce(hjid,rjid) as jid,
 coalesce(hsid,rsid) as sid,
 coalesce(hcount,0)+
   sum(case when rjid is not null then 1 else 0 end) as hcount
from
 history
 full outer join roster on (hjid=rjid and hsid=rosid)
group by hjid,rjid,hsid,rosid,hcount;

Tomasz Myrta