Re: SQL Query Newbie Help

On Fri, Mar 24, 2006 at 02:29:10PM -0800, Stephan Szabo wrote:
>
> On Fri, 24 Mar 2006, Julie Robinson wrote:
>
> > This works, but is there a better solution?
> >
> > select *
> > from quality_control_reset T
> > where date = (
> > select max(date)
> > from quality_control_reset
> > where qualitycontrolrange = T.qualitycontrolrange);
>
> If you can use PostgreSQL extensions (and don't care that you might not
> get two rows if two ids had the same date equaling the max date for a
> given range), maybe something like:
>
> select distinct on (qualitycontrolrange) id, date, qualitycontrolrange
> from quality_control_reset order by qualitycontrolrange,date desc;
>
>
> Otherwise, you might see how the above compares in plan to something like
> (not really tested):
>
> select T.* from quality_control_reset T inner join
> (select qualitycontrolrange, max(date) as date from quality_control_reset
> group by qualitycontrolrange) T2
> on (T.qualitycontrolrange = T2.qualitycontrolrange and T.date=T2.date);

BTW, I believe the new row operator fixes in 8.2 make it possible to use
them to do this kind of thing as well...
--
Jim C. Nasby, Sr. Engineering Consultant jnasby(at)pervasive(dot)com
Pervasive Software http://pervasive.com work: 512-231-6117
vcard: http://jim.nasby.net/pervasive.vcf cell: 512-569-9461