Thanks for raising another interesting topic. I had never considered the performance benefits of doing things this way, but have used the method for other reasons (sometimes you simply don't need a reference data table).

Anyway, using your example schema, I just thought I'd highlight the fact that the "traditional" result set of all errors for a/all users can also be generated using the bitwise method.

Cheers,

Daniel

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DECLARE @user-id int

SET @userid = 3

-- return all errors for a user using the bitwise method in a join

SELECT U.*, E.*

FROM Users U

JOIN Errors E

ON E.ErrorFlag & U.UserErrorFlag = E.ErrorFlag

WHERE U.Userid = @userid

-- return all errors for a user using a join to the many-to-many intermediate table

SELECT U.*, E.*

FROM Users U

JOIN UserErrors UE

ON UE.UserId = U.UserId

JOIN Errors E

ON E.ErrorId = UE.ErrorId

WHERE U.UserId = @userid