Why to raise an exception?

Question

Hello
I am trying to understand that why do we RAISE an Exception.
I was seeing some documentation. where it gave this example
(to check if any rows were updated or not, it uses SQL%NOTFOUND)
DECLARE
BEGIN
UPDATE Tablename
IF SQL%NOTFOUND
RAISE e_invalid_Item
END IF
COMMIT;
EXCEPTION
WHEN e_invalid_Item
DBMS_OUTPUT.PUT_LINE ('No such Item);
END;
I was thinking
why cant we simply use the if statement to display. like below
IF SQL%NOTFOUND
DBMS_OUTPUT.PUT_LINE('.................');
END IF
So why to raise an exception and then display DBMS_OUTPUT........
Why dont we just display it where it happened?
What is really and USE of raising an exception?
thank you

Answer 1

I am trying to understand that why do we RAISE an Exception."An exception is a runtime error or warning condition, which can be predefined or user-defined. Predefined exceptions are raised implicitly (automatically) by the runtime system. *User-defined exceptions must be raised explicitly by RAISE statements*. To handle raised exceptions, you write separate routines called exception handlers."
http://download.oracle.com/docs/cd/B19306_01/appdev.102/b14261/exception_definition.htm#LNPLS01316
http://www.oracle.com/pls/db102/homepage
http://www.oracle.com/pls/db112/homepage
You only catch exceptions when you expect them, and then deal with them, let them propagate to the caller.
Hopefully this (imo) classic 'rant' will make you understand better:
http://asktom.oracle.com/pls/apex/f?p=100:11:0::::P11_QUESTION_ID:1509245700346768268#tom1535781400346575552
Never ever swallow an exception by catching one and just 'dbms_output.put_line' it. Doing so, is the same as making success out of failure. Please read the link. It should give you ideas on how things (should) work.
Only catch exceptions you expect.