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Date: Tue, 24 Jun 2003 00:04:42 +0200
From: Tomasz Myrta <jasiek@klaster.net>
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To: Ryan <pgsql-sql@seahat.com>
Cc: pgsql-sql@postgresql.org
Subject: Re: aggregate question
References: <54717.65.102.128.233.1056394792.squirrel@fordparts.com>
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Dnia 2003-06-23 20:59, Użytkownik Ryan napisał:
> I know this one is simple enough.
> 
> I have two tables: packages and package_log.

<cut>

> I must be a total space case today because I can't hammer out the sql to
> get a listing of all the packages with a count() of the package_log by
> package_id.
> 
> Thanks,
> Ryan

select package_name,
  count(*) as n_packages
from
  packages
  join package_log using (package_id);

This query is the simplest one, but doesn't display packages without any logs.
If you need this, try this one:
select p.package_name,
  (select count(*) from package_log pl where pl.package_id=p.package_id)
    as n_packages
from packages p;

And one more:
select package_name,
  sum(case when package_log.package_id is not null then 1 else 0 end)
    as n_packages
from
  packages
  left join package_log using (package_id);


Regards,
Tomasz Myrta