Update trigger

Question

I have emp table. columns ename ,emp_type ,address etc
I can insert as many as record like ename 'john' and emp_type 'N'.. but i can only insert one record 'john' and emp_type 's'
so my when i do insert or update i want to check if record already exist for ename "JOHN" and type "S" if exist the don't allow to insert
but for update make sure again record alreday exist or not. if exist then display message.. else do update other columns
see my trigger below is not working proprly for update
ename --- emp_type ---- address
john --- N dddd
john ---- N ---- dddd
john ---- S ---- dddddd
but i can insert only one rec
create or replace trigger EMP_UPD
before insert on EMP
FOR EACH ROW
Declare
cnt number;
emp_type varchar2(30);
pragma autonomous_transaction;
begin
select count(*) into cnt from emp
where ename=:new.ename and emp_type='S';
if (cnt >= 1 and :New.emp_type='S') then
raise_application_error(-20001,'record exist');
end if;
end;

Answer 1

I don't mean to sound like a broken record here, but I believe this is the third time you've posted this question. This appears to be a duplicate of this thread
Re: Trigger
and this earlier thread
trigger
In both of those threads, various folks have told you that what you are trying to accomplish simply cannot be accomplished via triggers. This is a rather common problem, so the solutions are pretty well known. An index, as I and others have indicated, will do what you want. No matter how many times you ask the question, though, trigger based solutions are not going to work unless you can guarantee that your system will have only 1 active user or you want to get into some really convoluted solutions with shadow tables.
Justin
Distributed Database Consulting, Inc.
http://www.ddbcinc.com/askDDBC