Use parameters in an XOR fashion

Question

I have two parameters which should be used alternatively (either a value OR it's synonym).
It's not a problem if the user enters both - I just want to be sure that at least one parameter is entered (to avoid a full table scan).
I tried a condition "param-1 is not null or param-2 is not null" but this does not avoid the execution of a "useless" query.
Does anybody know a trick?
Susanne
PS: I'm using Discoverer v10.1.2
Message was edited by:
laloca

Answer 1

Hi,
All conditions are evaluated when the query is executed, bind variables are used to pass the parameters into the query. So the nvl() method or using the condition param1 is not null or param2 is not null will give you the result, but as you say it will not stop a 'useless' query being run.
If you what to stop the query being run when both params are empty then you need to look at using a raise_error function. For example, the following function raises a database error if message input is not null.
CREATE FUNCTION raise_error(p_message VARCHAR2) RETURN VARCHAR2
IS
BEGIN
IF p_message IS NOT NULL THEN
RAISE_APPLICATION_ERROR(-20001, p_message);
RETURN ('FALSE');
ELSE
RETURN ('TRUE');
END IF;
END raise_error;
You can then load the function into the EUL and create a condition that raises an error as soon as the condition is evaluated. This will be at the start of the query executing. e.g. raise_error(case when nvl(:param1, :param2) is null then 'Cannot have both parameters empty' end) = 'TRUE'. The query will then fail raising a database error if both parameters are null.
Hope that helps,
Rod West