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
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