How to check if a tuple exists

Question

Hello everybody,
I want to check in a pl/sql-tgrigger if a tuple exists in a table.
The logical idea is something like that:
IF :new.firstname NOT IN (SELECT firstname FROM customer) THEN
dosth;
END IF;
This construct is unfortunately not possible ;-)
What is the correct way to solve my problem?
Thanks in advance

Answer 1

Hello,
I understood your question in the following way
a) you want to check the firstname is
already existed or not
b) if not exists you want to execute
a procedure "dosth"
If I understood properly, follow the given method
Step 1: set feedback off
Step 2: alter table customer add unique(firstname);
Step 3: create or replace view customer_v
as select * from customer;
Step 4:
create or replace trigger exists_check
instead of insert on customer_v for each row
begin
insert into customer(firstname)
values(:new.firstname);
dosth;
exception
when dup_val_on_index then
dbms_output.put_line('Already Exists');
end;
Step 5: insert into customer_v(firstname)
values('scott');
(if "scott" already exists the trigger displays the message otherwise executes the procedure "dosth")
If any wrong in my understanding, please explain the question clearly.
Regards
Sailaja