Did you check out:
http://dev.mysql.com/doc/refman/5.0/en/create-trigger.html?
You should be able to find qhat you are looking for. You can also check out thesE:
http://mysql.gilfster.com/page.php?parent_id=2&page_id=2.0.1
To get a quick start:
create trigger air_update
after update on some_table
for each row
begin
if new.forename != old.forname then
insert
into db_log(table_name,event_date,id,user,event_type,field_name,old_value,new_value)
values ('some_table',current_timestamp(),new.id,session_user(),'Update','forename',old.forename,new.forename);
end if;
...
..etc..
..
end;
If you don't fancy writing all the code yourself, user the information_schema (http://dev.mysql.com/doc/refman/5.0/en/information-schema.html) to generate it for you (see
http://mysql.gilfster.com/page.php?parent_id=6&page_id=6.0.2
for such examples)
(BTW, the user that creates the trigger must have the SUPER privilege!)