Oracle Trigger to log changes in a table

Question

I have a situation where if a new record is created or a modification to a table is made all details of these changes are logged. For example
A change is made in a customer table, from
Customername - Andrew
Customerid - 1
to
Customername - John
Customerid - 1
The changes would be logged in a separate table of the following format
TableType - The table the edit or new record appeared in
Username - The user that made the change
ChangeDate - Date of change
Uniqueid - Customer id
change type - the type of change add or modify
colname - the column name affected by the change
oldvalue - the old value
newvalue - the new value
therefore for the above example the logtable would be populated as follows:
TableType - Customer
Username - athompson
ChangeDate - 17/01/06
Uniqueid - 1
change type - modify
colname - customername
oldvalue - andrew
newvalue - john
Ok that sums up the aim, all im wondering is if this is possible using Oracle Triggers?
Any help, advice or possible solutions would really be helpful as im a bit of a trigger newbie :P
cheers
AndyT

Answer 1

Ah okay, the system has been designed and built before all requirements are known and understood and now cannot be changed. This is a common reason for using triggers as a kludge to fill the gaps in the application after the fact.
Based on the low usage though you should probably be okay, hopefully this will help get you started.
Also see the SQL and PL/SQL Reference guides
http://download-east.oracle.com/docs/cd/B19306_01/server.102/b14200/toc.htm
http://download-east.oracle.com/docs/cd/B19306_01/appdev.102/b14261/toc.htm
SQL> create table t (n number);
Table created.
SQL> create table t_log (table_name varchar2(30),
  2    username varchar2(30), change_date date, change_type varchar2(10),
  3    old_value number, new_value number);
Table created.
SQL> create or replace trigger t_after_row
  2  after insert or update on t
  3  for each row
  4  declare
  5    l_type varchar2(10);
  6  begin
  7
  8    if updating then
  9      l_type := 'MODIFY';
10    elsif inserting then
11      l_type := 'ADD';
12    end if;
13
14    insert into t_log
15      (
16      table_name,
17      username,
18      change_date,
19      change_type,
20      old_value,
21      new_value
22      )
23    values
24      (
25      'T',
26      user,
27      sysdate,
28      l_type,
29      :old.n,
30      :new.n
31      );
32
33  end;
34  /
Trigger created.
SQL> insert into t values (1);
1 row created.
SQL> insert into t values (2);
1 row created.
SQL> update t set n = 3 where n = 1;
1 row updated.
SQL> select * from t_log;
TABLE_NAME   USERNAME     CHANGE_DAT CHANGE_TYP  OLD_VALUE  NEW_VALUE
T            TEST         01-19-2006 ADD                            1
T            TEST         01-19-2006 ADD                            2
T            TEST         01-19-2006 MODIFY              1          3
SQL>