Re: pgsql aggregate: conditional max

Daniel CAUNE wrote:

> SELECT aid, cat
>
>  FROM table, (
>    SELECT aid, max(weight) as weight
>      FROM table
>      GROUP BY aid) AS tablemaxweight
>  WHERE table.aid = tablemaxweight.aid
>    AND table.weight = tablemaxweight.aid;
>
>There is a limit case you don't specify how to deal with, when two or more categories have the same maximum weight.  The query I wrote retrieves all the categories that have the maximum weight, but perhaps you just want one per aid.
>  
>
Yes, this will introduce duplicates. Yet it is not too difficult to 
select only one for each aid from the results. Thank you!

Weimao

>--
>Daniel
>
>
>  
>


-- 
All best, 

Weimao

Weimao Ke
Indiana University Bloomington
School of Library and Information Science
http://ella.slis.indiana.edu/~wke