Question

I have a query that is currently using a correlated subquery to return the results, but I am thinking the problem could be solved more eloquently perhaps using ROW_NUMBER().

The problem is around the profile of a value v, through a number of years for an Item. Each item has a number of versions, each with its own profile whick starts when the version is introduced and the data currently looks like this:

     ItemId    ItemVersionId    Year    Value =========================================== 1         1                01      0.1 1         1                02      0.1 1         1                03      0.2 1         1                04      0.2 1         1                05      0.2 1         1                06      0.3 1         1                07      0.3 1         1                08      0.4 1         2                04      0.3 1         2                05      0.3 1         2                06      0.3 1         2                07      0.4 1         2                08      0.5 1         3                07      0.6 1         3                08      0.7 2         1                01      0.1 2         1                01      0.1 2         1                01      0.2 etc 

I want to return the full profile for an Item using the most recent version where applicable. For the above example for item 1:

 ItemId    ItemVersionId    Year    Value =========================================== 1         1                01      0.1 1         1                02      0.1 1         1                03      0.2 1         2                04      0.3 1         2                05      0.3 1         2                06      0.3 1         3                07      0.6 1         3                08      0.7 

I am currently using

SELECT ItemId, ItemVersionId, Year, Value FROM table t WHERE     ItemId = 1     AND ItemVersionId = (SELECT MAX(ItemVersionId) FROM table WHERE ItemId = t.ItemId AND Year = t.Year)    

Whilst this returns the correct I suspect there is a more efficient way to do it, especially when the table gets large.

I am using SQL Server 2005.

Thanks in advance

Answer 1

I would do it with a CTE:

WITH Result AS (   SELECT Row_Number() OVER (PARTITION BY ItemId, Year ORDER BY ItemversionId DESC) AS RowNumber       ,ItemId       ,ItemversionId       ,Year       ,Value   FROM table ) SELECT ItemId   ,ItemversionId   ,Year   ,Value FROM Result WHERE RowNumber = 1 ORDER BY ItemId, Year