Using dbms_output in Trigger

Question

hi
I asked my question previous;y but couldnt get an exact answer for my question
I have three table grade
grade(studentno,courseno,grade)
courses(courseno,coursename)
prerequisite(courseno,prereqcourseno)
prereq(courseno) is foreign key on courses(courseno)
I want to make I trigger that when one try to add a course in grade table
the trigger will check the prerequisite of that course
and if the course is not exist in grade table( which means student has not take the prereq before)
the trigger will give an error and will report the prerequisites that the student need for that course;
The problem is I cant show the prerequisite courses that the student need, when I insert a course without prerequisite.
for example let say prereq of course C is A and B
so when I try to insert A into grade, the trigger should say that u cant do it, because u nedd A and B
thanks in advance

Answer 1

I agree totally with Kamal Kishores opinion. even i discourage my friends , the usage of DBMS_OUTPUT package.
It should be used more or less as a tool for debugging. As a beginner it may be advantageous and easy to learn abt the
stored procedure programming. But keeping in view that PL/SQL is more used in the backend processing. Just keep in view that
we are using a front end tool and we are writing our programs in back end (PL/SQL) then the use of DBMS_OUTPUT package and
dependency on that is waste of efforts. infact the point of DBMS_OUTPUT using to output a big chunk of varchar2 string to the
client SQL*PLUS window may / may not be advantageous.
coz if we are using Windows client and using the DBMS_OUTPUT put display the message on the screen then we may not be seeing
the messages immediately on the screen unless the execution of the program is completed. For that we are using our debugging in a separate way.
Suppose if i want to know what is the program doing at the current instance of time , then it may not be possible using DBMS_OUTPUT package.
my debugging style is in this way. I have created a procedure with AUTONOMOUS TRANSACTION with a single arguement of VARCHAR2;
CREATE OR REPLACE PROCEDURE SEND_MES(MES VARCHAR2) IS
PRAGMA AUTONOMOUS_TRANSACTION;
BEGIN
INSERT INTO DEBUG_TRAP VALUES(MES,TO_CHAR(SYSDATE,'HH24-MI-SS'));
COMMIT;
end;
EVEN THOUGH IT MAY BE AN OVER HEAD but it is very very advantageous to findout how the program is behaving and
where the current control is in the program. i monitor the values inputted in the table DEBUG_TRAP using another session. which makes me easily understandable where my program is
and gives me idea how to improve / tune my program .
prakash