Re: SQL Question

["Julian Scarfe" <julian@xxxxxxxxxxx>]

From: "Alex" <alex@xxxxxxxxxxxxxxx>

> - How can i select only the newest record for each ProdId ?
>
> 100    | 2005-04-01
> 200    | 2005-04-01

DISTINCT ON was made for this and on the similar tables I have performs 
rather more efficiently than using a subquery.

select distinct on (ProdId) ProdId , LastUpdate
from produpdate
order by ProdId , LastUpdate desc;

> - How can i select to retrieve the last 2 dates in record
>
> 100    | 2005-04-01 | 2005-03-01
> 200    | 2005-04-01 | 2005-03-01

To get the previous one, my first thought is something like:

select distinct on (ProdId) ProdId , LastUpdate
from produpdate p1
where LastUpdate <> (
   select max(LastUpdate ) from produpdate p2 where p2.ProdId = p1.ProdId
)
order by ProdId , LastUpdate desc ;

but there may be a much more efficient way of getting the nth result in 
general.

Julian Scarfe 



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