[SQL] query: last N price for each product?

2008-07-04 Thread David Garamond 
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.

Regards,
dave

-- 
Sent via pgsql-sql mailing list (pgsql-sql@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-sql

Re: [SQL] query: last N price for each product?

2008-07-04 Thread Claus Guttesen 
> 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.

Will this work?

SELECT * FROM price p1
  WHERE ctime int (SELECT ctime FROM price p2 WHERE
p1.product_id=p2.product_id order by ctime desc limit 3)

-- 
regards
Claus

When lenity and cruelty play for a kingdom,
the gentlest gamester is the soonest winner.

Shakespeare

-- 
Sent via pgsql-sql mailing list (pgsql-sql@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-sql

Re: [SQL] query: last N price for each product?

2008-07-04 Thread Frank Bax 

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)



--
Sent via pgsql-sql mailing list (pgsql-sql@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-sql