From: | Frank Bax <fbax(at)sympatico(dot)ca> |
---|---|
To: | pgsql-sql(at)postgresql(dot)org |
Subject: | Re: query: last N price for each product? |
Date: | 2008-07-04 12:55:58 |
Message-ID: | 486E1DDE.6070801@sympatico.ca |
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Lists: | pgsql-sql |
David Garamond wrote:
> Dear SQL masters,
>
> The query for "latest price for each product" goes like this (which I
> can grasp quite easily):
>
> SELECT * FROM price p1
> WHERE ctime=(SELECT MAX(ctime) FROM price p2 WHERE p1.product_id=p2.product_id)
>
> or:
>
> SELECT * FROM price p1
> WHERE NOT EXISTS (SELECT * FROM price p2 WHERE
> p1.product_id=p2.product_id AND p1.ctime < p2.ctime)
>
> but how do yo query for "latest 3 prices for each product"? The
> "price" table contains current price as well as price histories.
Is this what you are looking for...
SELECT * FROM price p1
WHERE ctime in (SELECT ctime FROM price p2 WHERE
p1.product_id=p2.product_id ORDER BY ctime DESC LIMIT 3)
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