Exception inside Trigger in Oracle 11g XE causes ORA-04088 error - oracle

Question

I am learning how to write user-defined exceptions inside trigger using Oracle 11g XE and seems the answer for this question serves as a good example:
create or replace trigger trig1
before update
of sal
on emp
for each row
when (new.sal < old.sal)
declare
user_xcep EXCEPTION;
PRAGMA EXCEPTION_INIT( user_xcep, -20001 );
begin
raise user_xcep;
end;
/
However, when I try this an update a record with a value of sal lower than the original value, I get the following error:
Error starting at line : 24 in command -
update emp set sal = 1100 where id = 1001
Error report -
ORA-20001:
ORA-06512: at "USER01.TRIG1", line 5
ORA-04088: error during execution of trigger 'USER01.TRIG1'
I found from the Internet that this means a runtime error in the trigger code. But where is the problem? As the above code is from an answer written in 2013, because I am using a new version of Oracle, making the original trigger not working anymore? How should I fix it?

Answer 1

This happened because you need to specify what happened? when the custom error occurs:
Create Or Replace Trigger trig1
Before Update Of sal On emp
For Each Row
When (Nvl(new.sal, 0) < Nvl(old.sal, 0))
Declare
user_xcep Exception;
Pragma Exception_Init(user_xcep, -20001);
Begin
dbms_output.put_line('test');
Raise user_xcep;
Exception
When user_xcep Then
dbms_output.put_line('-'||sqlcode||' - '||sqlerrm);
When Others Then
dbms_output.put_line(sqlerrm);
End;
This you can defined using the Exception clause, first the custom errors and then the system errors like NO_DATA_FOUND, TO_MANY_ROWS and finally the OTHERS errors that catch any other error that occurr inside the trigger.
If you need to stop the program you can use the Raise_Application_Error inside the custom exception:
Raise_Application_Error(sqlcode, 'Custom Error Message');