Mutating triggers

I have a table that has a conditional unique constraint on it. Assume I have two columns: parm_code and code_value. If parm_code = 'A' then the code_value must be unique for all rows with parm_code='A'.
If parm_code != 'A' then the code value does not have to be unique. Hence, I cannot create a unique constraint on parm_code and code_value.

Therefore I created a database trigger to check if parm_code = 'A' then see if there are any other records with parm_code = 'A' and code_value = :new.code_value (and if there is I raise_application_error). The trigger works fine for an insert but mutates on an update. Is there a trick to doing something like this, or a better way?

Chris Halioris Received on Tue Jan 21 1997 - 00:00:00 CST