Two triggers on same table

Question

Hi Friend.
I have to write two triggers on same table for auditing different columns of different users(may be different modules).
I will have an audit table in which i will insert data such as (user_id,module_id,column_name,old_col_val,new_col_val,timestamp)
Now different users from different modules will update the data on same table may be same columns from different front end forms!
If we write directly, we will not be able to know which column is updated by which user.
My question is in this case how can we control the triggers to raise differently?

Answer 1

You can use WHEN clause to fire a trigger only when some condition is true - you can check an user also,
look at simple example:
- suposse we have two users US1 and US2:
C:\>sqlplus sys as sysdba
SQL*Plus: Release 10.2.0.1.0 - Production on Pn Gru 6 13:14:22 2010
Copyright (c) 1982, 2005, Oracle.  All rights reserved.
Enter password:
Connected to:
Oracle Database 10g Express Edition Release 10.2.0.1.0 - Production
SQL> create user us1 identified by us1;
User created.
SQL> create user us2 identified by us2;
User created.
SQL> grant connect, resource to us1, us2;
Grant succeeded.
SQL> grant create public synonym to us1, us2;
Grant succeeded.and suposse we have a table with three columns + audit table:
SQL> connect us1
Enter password:
Connected.
SQL> create table tab123(
  2  col1 number,
  3  col2 number,
  4  col3 number);
Table created.
SQL> create table audit_tab123(
  2  username varchar2(100),
  3  col1 number,
  4  col2 number,
  5  col3 number );
Table created.
SQL>  grant select, update, insert on tab123 to us2;
Grant succeeded.
SQL>  grant select, update, insert on audit_tab123 to us2;
Grant succeeded.
SQL> create public synonym tab123 for tab123;
Synonym created.
SQL> insert into tab123 values( 1, 1, 1 );
1 row created.
SQL> commit;
Commit complete.We want a trigger that is fired only by user US1 and only after update of COL1 and COL2
(COL3 is ignored):
SQL> connect us1/us1
Connected.
SQL> CREATE OR REPLACE TRIGGER Trig_123_US1
  2  AFTER UPDATE OF col1, col2 ON tab123
  3  FOR EACH ROW
  4  WHEN ( user = 'US1' )
  5  BEGIN
  6    INSERT INTO audit_tab123( username, col1, col2 )
  7    VALUES( user, :new.col1, :new.col2 );
  8 END;
SQL> /
Trigger created.And we want a second trigger that is fired only by user US2 and only after update of COL2 and COL3
(COL1 is ignored):
SQL> connect us1/us1
Connected.
SQL> CREATE OR REPLACE TRIGGER Trig_123_US2
  2  AFTER UPDATE OF col2, col3 ON tab123
  3  FOR EACH ROW
  4  WHEN ( user = 'US2' )
  5  BEGIN
  6    INSERT INTO audit_tab123( username, col2, col3 )
  7    VALUES( user, :new.col2, :new.col3 );
  8  END;
  9  /
Trigger created.and now let test our triggers:
SQL> connect us1/us1
Connected.
SQL> update tab123 set col1 = 22;
1 row updated.
SQL> update tab123 set col2 = 22;
1 row updated.
SQL> update tab123 set col3 = 22;
1 row updated.
SQL> commit;
Commit complete.
SQL> select * from audit_tab123;
USERNAME         COL1       COL2       COL3
US1                22          1
US1                22         22
SQL> connect us2/us2
Connected.
SQL> update tab123 set col1 = 333;
1 row updated.
SQL> update tab123 set col2 = 333;
1 row updated.
SQL> update tab123 set col3 = 333;
1 row updated.
SQL> commit
  2  ;
Commit complete.
SQL> select * from us1.audit_tab123;
USERNAME         COL1       COL2       COL3
US1                22          1
US1                22         22
US2                          333         22
US2                          333        333As you see, each trigger is fired only once, first triger only for user US1 and columns COL1 and COL2,
and second trigger only for user US2 and only after update of COL2 and COL3.
I hope this will help.