Best way to do nested case statement logic in SQL Server

Question

I\'m writing an SQL Query, where a few of the columns returned need to be calculated depending on quite a lot of conditions.

I\'m currently using nested case stateme

Answer 1

I personally do it this way, keeping the embedded CASE expressions confined. I'd also put comments in to explain what is going on. If it is too complex, break it out into function.

SELECT
    col1,
    col2,
    col3,
    CASE WHEN condition THEN
      CASE WHEN condition1 THEN
        CASE WHEN condition2 THEN calculation1
        ELSE calculation2 END
      ELSE
        CASE WHEN condition2 THEN calculation3
        ELSE calculation4 END
      END
    ELSE CASE WHEN condition1 THEN 
      CASE WHEN condition2 THEN calculation5
      ELSE calculation6 END
    ELSE CASE WHEN condition2 THEN calculation7
         ELSE calculation8 END
    END AS 'calculatedcol1',
    col4,
    col5 -- etc
FROM table

Answer 2

a user-defined function may server better, at least to hide the logic - esp. if you need to do this in more than one query

Answer 3

This example might help you, the picture shows how SQL case statement will look like when there are if and more than one inner if loops