Using t-sql to lookup value based on dates in other table - sql

Question

I have the following challenge. I have 2 tables. First table contains changes in values of bikes, at a certain moment (i.e. price catalogue). This means a certain price for a product is valid untl there is a new price within the table.
Product | RowNr | Year | Month | Value
------------------------------------------
Bike1 | 1 | 2009 | 8 | 100
Bike1 | 2 | 2010 | 2 | 400
Bike1 | 3 | 2011 | 4 | 300
Bike1 | 4 | 2012 | 9 | 100
Bike1 | 5 | 2013 | 2 | 500
Bike1 | 6 | 2013 | 5 | 200
Bike2 | 1 | 2013 | 1 | 5000
Bike2 | 2 | 2013 | 2 | 4000
Bike2 | 3 | 2014 | 6 | 2000
Bike2 | 4 | 2014 | 10 | 4000
The second table contains dates for which I would like to determine the value of a bike (based on the information in table 1).
Product | Date | Value
-------------------------
Bike1 | 3/01/2008 | ?
Bike1 | 04/30/2011 | ?
Bike1 | 5/08/2009 | ?
Bike1 | 10/10/2012 | ?
Bike1 | 7/01/2014 | ?
So line 1 and 3 should get value "400", line 2 "300", line 4 "100" and line 5 "200" etc.
Does anyone know how this can be achieved in T-SQL? I've already partitioned the first table, but could use some advice on the next steps.
Many thanks,

Answer 1

You could do something like this, which will retrieve the most recent price catalogue value for the product, using the price that is less than or equal to the product table date.
SELECT p.product
, p.date
, valueAsOfDate =
( SELECT TOP 1 c.value
FROM priceCatalogue c
WHERE c.product = p.product
AND convert(date,
convert(varchar(4), c.year) + '-'
+ convert(varchar(2), c.month)
+ '-1'
) <= p.date
--this order by will ensure that the most recent price is used
ORDER BY c.year desc, c.month desc
)
FROM product p
This table structure is not ideal... you would be better off with an "AsOfDate" column in your priceCatalogue table, so that you do not have to cast the values in the priceCatalogue table as a date in order to compare. If this is new development, change the priceCatalogue table to have an asOfDate column that is a date data type. If this is an existing table that is populated from another data source, then you could look at adding a persisted computed column to the table. http://msdn.microsoft.com/en-us/library/ms188300.aspx
With asOfDate column on the productCatalogue table, you have a SARG-able query (What makes a SQL statement sargable? ) that can take advantage of indexes.
SELECT p.product
, p.date
, valueAsOfDate =
( SELECT TOP 1 c.value
FROM priceCatalogue c
WHERE c.product = p.product
AND c.asOfDate <= p.date
--this order by will ensure that the most recent price is used
ORDER BY c.year desc, c.month desc
)
FROM product p

Answer 2

just use the YEAR() and MONTH() functions to take those parts of the date, and join them on your versioned table.
select
from product p
inner join productVersion pv
on p.product = pv.product
and Year(p.Date) = pv.Year
and Month(p.Date) = pv.Month

Answer 3

Xivan,
I think for both your line 1 and 3 it should get value "100" as 3/1/2008 and 5/8/2009 is less then 8/xx/2009.
As your table structure is not ideal, you have to create some computed columns for calculation.Hope the below query will work for you.
WITH cte
AS (
SELECT p.*
,(
SELECT min(p1.rownr) rownr
FROM product p1
WHERE p1.rownr > p.rownr
AND p.product = p1.product
GROUP BY p1.product
) AS nrownr
,(
SELECT max(p1.rownr) rownr
FROM product p1
WHERE p1.rownr < p.rownr
AND p.product = p1.product
GROUP BY p1.product
) AS prownr
FROM product p
)
SELECT pd.*
,c.value
FROM product_date pd
LEFT JOIN cte c ON pd.product = c.product
LEFT JOIN product p ON c.product = p.product
AND c.nrownr = p.rownr
LEFT JOIN product p1 ON c.product = p1.product
AND c.prownr = p1.rownr
WHERE (pd.DATE !> convert(DATE, convert(VARCHAR(4), (
CASE WHEN p.year IS NOT NULL THEN p.year ELSE 9999 END)) + '-' + convert(VARCHAR(2), (
CASE WHEN p.month IS NOT NULL THEN p.month ELSE 12 END)) + '-' + '1')
AND
pd.DATE !< convert(DATE, convert(VARCHAR(4), c.year) + '-' + convert(VARCHAR(2), c.month) + '-' + '1'))
OR
(pd.DATE !> convert(DATE, convert(VARCHAR(4), (
CASE WHEN p1.year IS NOT NULL THEN NULL ELSE 2009 END)) + '-' +
convert(VARCHAR(2), ( CASE WHEN p1.month IS NOT NULL THEN NULL ELSE 8 END)) + '-' +'1')
)
http://sqlfiddle.com/#!3/22c1d/2