From: David Johnston <polobo@yahoo.com>
To: John Fabiani <johnf@jfcomputer.com>
Cc: pgsql-sql@postgresql.org <pgsql-sql@postgresql.org>
Subject: Re: using the aggregate function max()
Date: Thu, 22 Sep 2011 23:14:58 -0400
Message-ID: <5EABD4DE-5CB8-4C65-A1FF-3166A683EE3F@yahoo.com> (raw)
In-Reply-To: <201109221949.20671.johnf@jfcomputer.com>
References: <201109221949.20671.johnf@jfcomputer.com>
On Sep 22, 2011, at 22:49, John Fabiani <johnf@jfcomputer.com> wrote:
> Hi,
> I need a little help understanding how to attack this problem.
>
> I need to find the max(date) of a field but I need that value later in my
> query.
>
> If I
> select max(x.date_field) as special_date from (select date_field) from table
> where ...)x
>
> I get one row and column.
>
> But now I want to use that field in the rest of the query
>
> select y.*, max(x.date_field) as special_date from (select date_field) from
> table where ...)x
> from aTable y where y.somefield = special_date.
>
> The above only returns one row and one column the "special_date."
>
> How can I use the aggregate field "special_date" in the rest of the query? Or
> is there some other way?
>
> Johnf
>
> --
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Your query above is syntactically invalid. Try this.
WITH max_date AS ( select max(datefield) AS specialdate from ...)
SELECT *
FROM table
JOIN max_date ON table.somefield = max_date.specialdate;
You can use a online query instead of the WITH if desired, same effect.
You could also drop the join and use the max_date CTE in a WHERE clause:
... FROM table WHERE table.somefield = (SELECT specialdate FROM max_date)
David J
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To: pgsql-sql@postgresql.org
Cc: polobo@yahoo.com, johnf@jfcomputer.com
Subject: Re: using the aggregate function max()
In-Reply-To: <5EABD4DE-5CB8-4C65-A1FF-3166A683EE3F@yahoo.com>
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