Question

I have a query that looks like this, and which is getting a percentage:

SELECT SUM(convert(decimal(3,2),
          CASE WHEN Status_ID = 1 AND State_ID = 14 THEN 1 ELSE 0 END))/
          SUM(convert(decimal(3,2),CASE WHEN State_ID = 14 THEN 1 ELSE 0 END)) * 100
FROM SomeTable

This may return something like 59.77803 in a normal case. But it turns that there are (rightly) cases when the second SUM — the denominator — could be 0. Does anyone know of a way to account for this case and avoid a divide by 0 exception?

I’m using SQL Server 2005. Thanks.

Answer 1

I would probably use a NULL to represent uncalculatable, but it depends upon your intent in your problem domain (code expanded to show what’s going on):

SELECT SUM(convert(decimal(3,2),
                   CASE WHEN Status_ID = 1 AND State_ID = 14 THEN 1 ELSE 0 END)
          )
       /
       NULLIF(
           SUM(convert(decimal(3,2),
                       CASE WHEN State_ID = 14 THEN 1 ELSE 0 END)
           )
           , 0
       )
       * 100
FROM SomeTable

The result when there are no rows in the table so the denominator would be zero – gets converted to NULL so the whole expression ends up NULL.

That code can also be simplified a little (probably because it’s already a simplified toy problem):

SELECT SUM( convert(decimal(3,2), CASE WHEN Status_ID = 1 THEN 1 ELSE 0 END) )
       /
       NULLIF( convert(decimal(3,2), COUNT(*)), 0 )
       * 100
FROM SomeTable
WHERE State_ID = 14

As an example of combining a number of different things into one query:

SELECT CASE WHEN State_ID = 14 THEN 'State_ID = 14'
            WHEN State_ID IN (1, 2, 3) THEN 'State_ID IN (1, 2, 3)'
            ELSE 'DEFAULT'
       END AS Category
       ,SUM(convert(decimal(3,2),
                   CASE WHEN Status_ID = 1 THEN 1 ELSE 0 END)
          )
       /
       convert(decimal(3,2), COUNT(*))
       * 100
FROM SomeTable
GROUP BY CASE WHEN State_ID = 14 THEN 'State_ID = 14'
            WHEN State_ID IN (1, 2, 3) THEN 'State_ID IN (1, 2, 3)'
            ELSE 'DEFAULT'
       END