Query on trigger.

Question

create or replace trigger trig_name before update of sal on emp for each row
Declare
excep exception;
begin
if (:new.sal=3500) then
dbms_output.put_line('value is more than 3500 okay');
else
--:new.sal:=3500
--update emp set sal=3500 where empno=:new.empno;
raise excep;
--raise_application_error(-20400,'update can''t be done');
--dbms_output.put_line('now sal value is set to 3500');
end if;
exception
when excep then
dbms_output.put_line('update can''t be done');
end;
in the above trigger I want to raise when updating sal is not equal to 3500.
1)Actually my intention is if it is not 3500 i want to make it ti 3500 and update it.. So I tried assigning 3500 to :new.sal(it gav error so left it)
2)then for the same i row i gav another update statement inside trigger body with sal=3500(it raised mutating error)
3) so I cudn't update the value i intented I decided to stop the update by raising a exception whenever sal vaue is not 3500..(this raises the given exception and at the same updates the value in the table)..
Please help me if I have to do above three transactions using trigger...
As I am abeginner pls excuse me if i have made any basic mistakes...
thanks in advance..
by
Prabu....

Answer 1

(this raises the given exception and at the same updates the value in the table)..That's because you trapped the exception in your exception...uhh...handler.
Get rid of your entire exception section. It's hiding your errors.
SQL> select * from t;
                   C
                   3
SQL> create or replace
  2  trigger tr
  3  before update of c on t
  4  for each row
  5  begin
  6     if :new.c = 0 then
  7        raise_application_error(-20400,'c can never be 0');
  8     end if;
  9  exception
10     when others then null;  --< one of the worst lines in all pl/sql
11  end;
12  /
Trigger created.
SQL> update t set c = 0;
1 row updated.
SQL> select * from t;
                   C
                   0