Creating a trigger for update

Question

I have a table that consists of the following: product_id number, location number, qty number. product_id and location are primary keys.
I want to create a trigger before an update and if the record doesn't exist that is trying to be updated, then I have to create the record.
For example, if I want to do an update of the following:
update inventory set qty = 80 where product_id=13 and location=45;
Let's say that the record doesn't exist, how do I do this with a trigger.

Answer 1

Hi,
First of all i would like to clear one thing:
IF you are trying to update any record and that record does not exist in table then trigger will not be called.
"afiedt.buf" 10 lines, 236 characters
  1  CREATE OR REPLACE TRIGGER t_trig
  2  BEFORE UPDATE ON t
  3    FOR EACH ROW
  4    BEGIN
  5             DBMS_OUTPUT.PUT_LINE('Trigger has been  called!!!');
  6    EXCEPTION
  7       WHEN OTHERS THEN
  8               DBMS_OUTPUT.PUT_LINE('IN EXCEPTION:'||SQLERRM);
  9*  END;
SQL>/
Trigger created.
SQL>DESC t;
Name                                      Null?    Type
NAME                                               VARCHAR2(20)
SQL>SELECT * FROM t;
NAME
BBB
1 row selected.
SQL>SET SERVEROUTPUT ON
SQL>
SQL>UPDATE t SET NAME='XXX' WHERE name='AAA';
0 rows updated.
SQL>UPDATE t SET NAME='XXX' WHERE name='BBB';
Trigger has been  called!!!  <-- Trigger called here
1 row updated.So to achieve your result you have to do it outside the trigger.
If you are updating trougha a procedure, after update statement you can use SQL%ROWCOUNT to get how many rows have been updated. If it zero you can insert the record.
Regards