How to aggregate a bit column

This is an oldie but a goodie:

When you first try to count the number of true values in a bit column (in SQL Server) you get this error:

"The sum or average aggregate operation cannot take a bit data type as an argument."

(caused by a query such as...

"SELECT SUM(MyBitField) FROM MyTableWhatHasABitColumn")

With droyad's help we came up with four ways to get around the problem:

SELECT
        SUM(CAST(MyBitField AS INT)) AS '1st Technique',
        SUM(CASE(MyBitField) WHEN 1 THEN 1 ELSE 0 END) AS '2nd Technique',
        COUNT(NULLIF(MyBitField,0)) AS '3rd Technique',
FROM
        MyTableWhatHasABitColumn

4th Technique: Another approach is to get a bigger hammer. In SQL Server 2005 you can create user defined aggregates, in the .net language of your choice. But that was the specific path I was trying to avoid going down.

Comparing the performance of these four techniques is left as an exercise for the avid reader. My favourite is the "COUNT NULLIF." I hope it ain't too slow.

(sorry for the straight nerd talk. not feel like telling funny stories this week)

 

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