Let's say there's an index on the date column: Does the where clause
approach necessarily out perform the distinct on version? Hoping the OP
has enough data to make analyse useful.
A. Kretschmer wrote:
> In response to Louis-David Mitterrand :
>
>> Hi,
>>
>> I have a simple table
>>
>> price(id_product, price, date)
>>
>> which records price changes for each id_product. Each time a price
>> changes a new tuple is created.
>>
>> What is the best way to select only the latest price of each id_product?
>>
>
> There are several ways to do that, for instance with DISTINCT ON (only
> postgresql):
>
> test=*# select * from price ;
> id_product | price | datum
> ------------+-------+------------
> 1 | 10 | 2009-09-01
> 1 | 12 | 2009-09-10
> 2 | 11 | 2009-09-10
> 2 | 8 | 2009-09-13
> (4 rows)
>
> test=*# select distinct on (id_product) id_product, price from price order by id_product, datum desc;
> id_product | price
> ------------+-------
> 1 | 12
> 2 | 8
> (2 rows)
>
> Andreas
>
