Need to use one and one only of multiple parameters in a stored procedure The issue is that I have 4 parameters for the user to select, and he/she can only choose one of the four.  In my current WHERE clause I have this logic... 

WHERE (PARAMETER1 = DBFIELD1
    OR PARAMETER2 = DBFIELD2
    OR PARAMETER3 = DBFIELD3
    OR PARAMETER4 = DBFIELD4)


But this brings back all the rows in the db.  I need to somehow NULL out the parameters that are not being used.  Is that possible within the WHERE clause?
I think something like the following pattern might work:

WHERE
  (PARAMETER1 = DBFIELD1 AND PARAMETER2 IS NULL AND PARAMETER3 IS NULL AND PARAMETER4 IS NULL)
  OR (PARAMETER2 = DBFIELD2 AND PARAMETER1 IS NULL AND PARAMETER3 IS NULL AND PARAMETER4 IS NULL)
  OR ...


That pattern is pretty ugly but it will only give you rows if one parameter is set and the others are null. In order to give you something more I'd need you to edit your question to better explain what you want.