"An autonomous transaction does not see any changes made by main transact"

Question

Hi,
I'm trying to reproduce the "An autonomous transaction does not see any changes made by main transaction" reffered on :
Oracle® Database Application Developer's Guide - Fundamentals
10g Release 2 (10.2)
Part Number B14251-01
chapter 2 SQL Processing for Application Developers
Paragraph : Autonomous TransactionsI set up a simple case...
create table emp_ as select * from emp
begin
  update emp_ set hiredate=hiredate+100 where empno=7934;
end;
create or replace trigger trg_emp_
after insert or update on emp_
for each row
declare
    pragma autonomous_transaction;
    emp_var emp.hiredate%type;
  begin
    select hiredate
      into emp_var
      from emp_
    where empno=:new.empno;
    dbms_output.put_line('empno: '||:new.empno);
    dbms_output.put_line('old hiredate: '||:old.hiredate);
    dbms_output.put_line('new hiredate: '||:new.hiredate);
  end;Prior to any change...
SQL> select empno,hiredate from emp_;
EMPNO HIREDATE
5498 21/4/1982
5499 11/10/1981
5411 10/10/1981
5410 10/10/1982
7369 17/12/1980
7499 20/2/1981
7521 22/2/1981
7566 2/4/1981
7654 28/9/1981
7698 1/5/1981
7782 9/6/1981
7788 19/4/1987
7839 17/11/1981
7844 8/9/1981
7876 23/5/1987
7900 3/12/1981
7902 3/12/1981
7934 23/1/1982After the change...
SQL> begin
  2    update emp_ set hiredate=hiredate+100 where empno=7934;
  3  end;
  4  /
empno: 7934
old hiredate: 23/01/82
new hiredate: 03/05/82
PL/SQL procedure successfully completedAccording to the Oracle doc the select of the autonomous transaction should not see the change made to the hiredate column of the table in the main transaction(in the anonymous block)....
What may i do wrong..????
Thank you,
Sim

Answer 1

Simon:
As Tubby pointed out, your dbms_output commands do not display the value you selected in the trigger. Your trigger based demonstration needs to be more like:
SQL> SELECT * FROM t;
        ID DT
         1 05-SEP-2009
         2 17-JUL-2009
SQL> CREATE TRIGGER t_ai
  2     AFTER INSERT OR UPDATE ON t
  3     FOR EACH ROW
  4  DECLARE
  5     PRAGMA AUTONOMOUS_TRANSACTION;
  6     l_dt t.dt%TYPE;
  7  BEGIN
  8     SELECT dt INTO l_dt
  9     FROM t
10     WHERE id = :new.id;
11     DBMS_OUTPUT.Put_Line ('ID: '||:new.id);
12     DBMS_OUTPUT.Put_Line ('Old dt: '||:old.dt);
13     DBMS_OUTPUT.Put_Line ('New dt: '||:new.dt);
14     DBMS_OUTPUT.Put_Line ('Aut dt: '||l_dt);
15  END;
16  /
Trigger created.
SQL> UPDATE t SET dt = sysdate WHERE id = 2;
ID: 2
Old dt: 17-JUL-2009
New dt: 25-OCT-2009
Aut dt: 17-JUL-2009
1 row updated.So, the automomous transaction select did not see the changed value of dt.
I know you are just trying to understand automomous transactions here and would never do sometihg like this in production right? :-)
Your trigger, as written, has some interesting side effects because of the automomous transaction. For example:
SQL> INSERT INTO t VALUES(3, sysdate - 25);
INSERT INTO t VALUES(3, sysdate - 25)
ERROR at line 1:
ORA-01403: no data found
ORA-06512: at "OPS$ORACLE.T_AI", line 5
ORA-04088: error during execution of trigger 'OPS$ORACLE.T_AI'
SQL> UPDATE t SET id = 3 where trunc(dt) = TO_DATE('05-Sep-2009', 'dd-mon-yyyy');
UPDATE t SET id = 3 where trunc(dt) = TO_DATE('05-Sep-2009', 'dd-mon-yyyy')
ERROR at line 1:
ORA-01403: no data found
ORA-06512: at "OPS$ORACLE.T_AI", line 5
ORA-04088: error during execution of trigger 'OPS$ORACLE.T_AI'John