Getting the average of two cols into third col when user inserts or updates

Question

I hav a table with three column a,b,c.
now i have to insert the average of the col a & b into c when user inserts or updates
any of the row?
i tried using row level trigger for this but not workin fine..
can anybody of u give me an idea as how to proceed?
thanks in advance..

Answer 1

Sorry to be late to reply....
actually..for the trigger i used i got a mutating error.
if there is any other option for doing this,u teel me how.
i used the followin trigger and placed AT to avoid the mutating error.But still
create or replace trigger trg_xyz after insert or update of m1,m2
on xyz for each row
declare
v1 number;
pragma autonomous_transaction;
begin
v1 := (:new.m1+:new.m2)/2;
if inserting then
update set m3=v1 where m2=:new.m2 and m1=:new.m1;
elsif updating then
update set m3=v1 where m2=:new.m2 and m1=:new.m1;
end if;
commit;
end;
this does not throw any error, but doesnt inserts the value.i checked using dbms_output..i showed the average value for v1..but its not updating..