On 2012-05-21 1:17 AM, Jan Bakuwel wrote:
Hi,
I'm trying to get my head around the following question. As an example
take a table with products:
productid (pk)
name
and productprice
productpriceid (pk)
productid (fk)
pricedate
price
There are multiple records in productprice for each product as prices
(often) go up and (less often) go down.
I'm looking for a query that returns the following:
productid, name, pricedate, current_price, difference
current_price is the latest (ie. most recent date) price of the product
and difference is the difference in price between the latest price and
the price before the latest.
Any suggestions how to do this with SQL only? I can make it work with a
function (probably less efficient) but think this should be possible
with SQL too...
cheers,
Jan
With windowing functions:
select FRS.name
,FRS.productprice as current_price
,FRS.productprice- NXT.productprice
from
(
SELECT PRC.productid
,PRC.productprice
,ROW_NUMBER() OVER(PARTITION BY PRC.productid ORDER BY
PRC.pricedate desc) rank_nr
FROM productprice PRC
,products PRD
WHERE 1 = 1
AND PRD.productid = PRC.productid
) FRS
LEFT JOIN
(
SELECT productid
,productprice
,ROW_NUMBER() OVER(PARTITION BY productid ORDER BY pricedate
desc) rank_nr
FROM productprice
) NXT
ON FRS.productid = NXT.productid
AND NXT.rank_nr < 3
AND FRS.rank_nr <> NXT.rank_nr
WHERE 1 = 1
AND FRS.rank_nr = 1
Without windowing functions (slightly complicated, it's merely a max-mix
issue and assuming that the date includes the time)
SELECT CUR.name
,CUR.productid
,CUR.current_price
,CUR.current_price - PRV.previous_price price_difference
FROM ( --LATEST PRICE
SELECT PRD.name
,PRC.productid
,PRC.productprice current_price
FROM productprice PRC
,products PRD
,(--LATEST PRICEDATE
SELECT productid
,MAX(pricedate) pricedate
FROM productprice
GROUP BY productid
) MMX
WHERE 1 = 1
AND PRC.productid = PRD.productid
AND PRC.productid = MMX.productid
AND PRC.pricedate = MMX.pricedate
)CUR
-- IN CASE THERE'S NO PREVIOUS PRICE
LEFT JOIN
( -- PREVIOUS PRICE
SELECT PRC.productid
,PRC.productprice previous_price
FROM productprice PRC
,(--PREVIOUS PRICEDATE
SELECT PRC.productid
,MAX(PRC.pricedate) pricedate
FROM productprice PRC
,(
SELECT productid
,MAX(pricedate) pricedate
FROM productprice
GROUP BY productid
) MMX
WHERE 1 = 1
AND PRC.productid = MMX.productid
AND PRC.pricedate < MMX.pricedate
) PRV
WHERE 1 = 1
AND PRC.productid = PRV.productid
AND PRC.pricedate = PRV.pricedate
) LST
ON CUR.productid = LST.productid
cheers
Mario
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