Re: Selecting All Columns Associated With Maximum Value of One Column

On Oct 6, 2011, at 9:34, Rich Shepard <rshepard(at)appl-ecosys(dot)com> wrote:

> On Wed, 5 Oct 2011, David Johnston wrote:
>
>> 2) "Window" - max(quant) OVER (PARTITION BY ...)
>
> Hmm-m-m. I have a problem here emulating the example on the document page.
> Regardless of which column is first after SELECT postgres tells me that
> column does not exist.
>
> select site_id, sample_date, param, max(quant) over (partition by param)
> chemistry;
> ERROR: column "site_id" does not exist
> LINE 1: select site_id, sample_date, param, max(quant) over (partiti...

Missing the FROM before chemistry

> ^
> select str_name, site_id, sample_date, param, max(quant) over (partition by
> str_name) chemistry;
> ERROR: column "str_name" does not exist
> LINE 1: select str_name, site_id, sample_date, param, max(quant) ove...
> ^
> What am I doing incorrectly here?
>
> Also, with the window function can I limit the output to a single str_name
> and param?

Not directly. After you create the windowed result you can turn it into a sub-query and filter that. The other form suggested (where quant = select max(quant) from chemistry where ...) is probably a better performer though for your need - I did't read the subject line closely enough and my two options don't directly give you what you are looking for. Though era ing the window query and then adding a (where quant_max = quant) clause would get you closer; quant_max being the column alias for the window expression.

>
> Rich
>

David J.