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Re: subquery question

From: Richard Broersma <richard(dot)broersma(at)gmail(dot)com>
To: Tom Raney <twraney(at)comcast(dot)net>
Cc: pgsql-novice(at)postgresql(dot)org
Subject: Re: subquery question
Date: 2009-02-01 03:58:56
Message-ID: (view raw, whole thread or download thread mbox)
Lists: pgsql-novice
On Sat, Jan 31, 2009 at 4:13 PM, Tom Raney <twraney(at)comcast(dot)net> wrote:

> I've dug around on the Postgres lists for a bit and I haven't found a good
> explanation of why this query is not allowed.

> WHERE Temp.count_agents = (SELECT MIN (Temp.count_agents) FROM Temp)

At this point, the sub-select on Temp wont work because Temp does
exist at its level of scope.  It don't fully understand how to use 8.4
new CTE feature, but I might allow something like this to work.  Using
SQL-92, you can make this work using two level of aggregation and
joining the result back to the original table.

SELECT Temp.team_id, Temp.count_agents
  FROM (SELECT TR.team_id, COUNT(TR.agent_id) AS count_agents
          FROM teamrel TR
      GROUP BY TR.team_id ) AS Temp
 WHERE Temp.count_agents = (SELECT MIN( teamcount )
                              FROM ( SELECT COUNT(*) AS teamcount
                                       FROM Teamrel
                                   GROUP BY T1.team_id ));

Richard Broersma Jr.

Visit the Los Angeles PostgreSQL Users Group (LAPUG)

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