After and before triggers

Question

My doubt is about the execution of triggers
I have a table T1
create table T1
+(ID1 number(9,2) primary key,+
NAME1 VARCHAR2(100)) ;
It has following 2 rows.
insert into t1 values (1,'sandeep')
insert into t1 values (2,'tom')
commit;
I have following 4 triggers
create or replace
TRIGGER TRIGGER1_before_statement
before update on T1
begin
dbms_output.put_line('fired before statement');
END;
create or replace
trigger TRIGGER_BEFORE_EACHROW
before update on T1 for each row
begin
DBMS_OUTPUT.PUT_LINE('fired before each row');
END;
create or replace
TRIGGER TRIGGER_after_eachrow
after update ON T1
FOR EACH ROW
begin
DBMS_OUTPUT.PUT_LINE('fired trigger after eachrow');
END;
create or replace
trigger TRIGGER1_AFTER_STATEMENT
after update on T1
begin
dbms_output.put_line('fired after statement');
END;
i ran the following script
SET SERVEROUTPUT ON;
begin
update T1 set T1.ID1=1 where T1.ID1 = 2;
end;
This update statement will fail because it violates the primary key constraint on the table.
During execution of the update statement, i expect only the before statement and row triggers to fire because after triggers will be fired after execution of the statement and in this case the update execution has failed.
But the output i am getting is
fired before statement
fired before each row
fired trigger after eachrow
which means the after TRIGGER_after_eachrow has also fired but my update statement has failed and TRIGGER_after_eachrow should fire only after updating the rows.
Why this trigger was fired? If oracle processes all the triggers even if the triggerig statement fails, then why TRIGGER1_AFTER_STATEMENT was not fired.
Thanks in advance.

Answer 1

Hi Sandeep,
While trying to search for the answer to your after trigger execution related issue, I got below from asktom site where I got a discussion regarding the same topic.
http://asktom.oracle.com/pls/asktom/f?p=100:11:0::::P11_QUESTION_ID:29259877603106
Below is the exact question post by one member and answer by tom in it.
I thought
Here is some sample which shows that after row statement fires event though the integrity
constraint check should have failed first.
Me and my colleagues are confused with the definition found at
http://download-uk.oracle.com/docs/cd/B19306_01/server.102/b14220/triggers.htm#sthref3288
drop table emp;
drop table dept;
-- Create table
create table DEPT
  ID    NUMBER not null,
  name VARCHAR2(100)
alter table DEPT add primary key (ID);
create table EMP
  ID      NUMBER not null,
  NAME    VARCHAR2(100),
  DEPT_ID NUMBER
alter table EMP
  add primary key (ID);
alter table EMP
  add constraint EMP_DEPT_FK foreign key (DEPT_ID)
  references DEPT (ID);
create or replace trigger EMP_AFT_INS_ROW_TRG after insert on emp  for each row
declare
    n number;   
begin
    select 1 into n from dept where dept.id = :new.dept_id;
exception
    when no_data_found then
        raise_application_error(-20001, 'No such department');
end;
insert into dept(id, name) values (1,'First department');
commit;
insert into emp (id, name, dept_id) values (101, 'First employee', 1);
commit;
rem here I expect a foreign key violation message instead of 'No such department' application error
insert into emp (id, name, dept_id) values (102, 'Second employee', 2);
commit;
Followup   September 5, 2006 - 5pm Central time zone:
constraints technically are validated AFTER the statement executes - it is not really defined
whether a trigger will or will not fire (and if you have logic that depends on such intricate
ordering, we have a really big logic problem)
but a for each row trigger - sure, because tables are allowed to violate their constraints during
the DML, think about this:
update emp set empno = empno+1;
every row updated could temporarily violate uniqueness as there could be two empno =2, empno=3 and
so on as this goes through row by row. May be its useful to you..
Regards,
Dipali..