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 statements, but its getting messy. Is there a better (more organised and/or readable) way?

(I am using Microsoft SQL Server, 2005)

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A simplified example:

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                 END AS 'calculatedcol1',     col4,     col5 -- etc FROM table 

Answer 1

You could try some sort of COALESCE trick, eg:

 SELECT COALESCE(   CASE WHEN condition1 THEN calculation1 ELSE NULL END,   CASE WHEN condition2 THEN calculation2 ELSE NULL END,   etc... )