Oracle/PLSQL: BEFORE INSERT Trigger

A BEFORE INSERT Trigger means that Oracle will fire this trigger before the INSERT operation is executed.

The syntax for an BEFORE INSERT Trigger is:

CREATE or REPLACE TRIGGER trigger_name
BEFORE INSERT
   ON table_name
   [ FOR EACH ROW ]

DECLARE
   -- variable declarations

BEGIN
   -- trigger code

EXCEPTION
   WHEN ...
   -- exception handling

END;

trigger_name is the name of the trigger to create.

Restrictions

• You can not create a BEFORE trigger on a view.
• You can update the :NEW values.
• You can not update the :OLD values.

For Example

If you had a table created as follows:

CREATE TABLE orders
( order_id number(5),
  quantity number(4),
  cost_per_item number(6,2),
  total_cost number(8,2),
  create_date date,
  created_by varchar2(10)
);

We could then create a BEFORE INSERT trigger as follows:

CREATE OR REPLACE TRIGGER orders_before_insert
BEFORE INSERT
   ON orders
   FOR EACH ROW
   
DECLARE
   v_username varchar2(10);
   
BEGIN

   -- Find username of person performing INSERT into table
   SELECT user INTO v_username
   FROM dual;
   
   -- Update create_date field to current system date
   :new.create_date := sysdate;
   
   -- Update created_by field to the username of the person performing the INSERT
   :new.created_by := v_username;
   
END;