Before or After Triggers

Question

Hi,
I have a doubt on functioning of Before or After Triggers.
Here is an example of it:
I created a trigger on EMP table
create or replace trigger tri11 before insert or update or delete on emp for each row
begin
if to_char(sysdate,'dy')='fri' then
raise_application_error(-20101,'No Transactions should be happend on Friday');
end if;
end;
According to the trigger created it has to fire before any event is happening and it should not allow any insertions or updates or deletion on FRIDAY.
And that is working fine.
I changed the trigger to fire on After Insert or update or delete....
create or replace trigger tri11 after insert or update or delete on emp for each row
begin
if to_char(sysdate,'dy')='fri' then
raise_application_error(-20101,'No Transactions should be happend on Friday');
end if;
end;
Here according to this trigger it has to fire after any event is happening .....but still it is not allowing me to perform any insertions or updates or deletion on FRIDAY.
And showing me the error message as below:
SQL> update emp set sal = 11000;
update emp set sal = 11000
ERROR at line 1:
ORA-20101: No Transactions should be happend on Friday
ORA-06512: at "SCOTT.TRI11", line 3
ORA-04088: error during execution of trigger 'SCOTT.TRI11'
Can anyone please explain me the difference.
Thanks.

Answer 1

All triggers must be fired synchronously with the triggering statement. The statement and all triggers that are fired as the result of the statement must be atomic-- they must all succeed or all fail. It doesn't matter whether it is a before or after statement trigger that throws the exception-- in either case, the entire statement will fail and thus be rolled back.
Justin