Message-ID: <4648EE4F.3040005@polimetrix.com>
Date: Mon, 14 May 2007 16:18:39 -0700
From: Geoff Tolley <geoff@polimetrix.com>
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To: Bryce Nesbitt <bryce1@obviously.com>
CC: pgsql-sql@postgresql.org
Subject: Re: Doing a conditional aggregate (e.g. count(*) if x=y) in postgres?
References: <4648E8F1.4020609@obviously.com>
In-Reply-To: <4648E8F1.4020609@obviously.com>
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Bryce Nesbitt wrote:
> All;
> Is there a way to get a conditional aggregate?  I have this two column view:
> 
>  SELECT count(*) AS count, xx_plan.plan_name
>    FROM xx_membership
>    JOIN xx_account USING (account_id)
>    JOIN xx_plan USING (plan_id)
>   WHERE xx_membership.status = 10
>   GROUP BY xx_plan.plan_name;
> 
> And would like to add additional columns (not rows) breaking out
> "status=20" and "status=30" totals.
> Is this possible without a stored procedure?

SELECT sum(CASE WHEN xx_membership.status = 10 THEN 1 ELSE 0 END) AS sum10,
        sum(CASE WHEN xx_membership.status = 20 THEN 1 ELSE 0 END) AS sum20,
        sum(CASE WHEN xx_membership.status = 30 THEN 1 ELSE 0 END) AS sum30,
        xx_plan.plan_name
   FROM xx_membership
   JOIN xx_account USING (account_id)
   JOIN xx_plan USING (plan_id)
  WHERE xx_membership.status IN (10,20,30)
  GROUP BY xx_plan.plan_name;

You may or may not care about including the WHERE clause there depending 
upon its selectivity and whether there's an index for the planner to use.

HTH,
Geoff