Re: using the aggregate function max()

On Sep 22, 2011, at 22:49, John Fabiani <johnf(at)jfcomputer(dot)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