Learn how to create a BEFORE DELETE Trigger in Oracle with syntax and examples.
A BEFORE DELETE Trigger means that Oracle will fire this trigger before the DELETE operation is executed.
The syntax to create a BEFORE DELETE Trigger in Oracle/PLSQL is:
CREATE [ OR REPLACE ] TRIGGER trigger_name BEFORE DELETE ON table_name [ FOR EACH ROW ] DECLARE -- variable declarations BEGIN -- trigger code EXCEPTION WHEN ... -- exception handling END;
OR REPLACE is optional. If specified, it allows you to re-create the trigger is it already exists so that you can change the trigger definition without issuing a DROP TRIGGER statement.
trigger_name is the name of the trigger to create.
BEFORE DELETE indicates that the trigger will fire before the DELETE operation is executed.
table_name is the name of the table that the trigger is created on.
Let's look at an example of how to create an BEFORE DELETE trigger using the CREATE TRIGGER statement.
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) );
We could then use the CREATE TRIGGER statement to create an BEFORE DELETE trigger as follows:
CREATE OR REPLACE TRIGGER orders_before_delete BEFORE DELETE ON orders FOR EACH ROW DECLARE v_username varchar2(10); BEGIN -- Find username of person performing the DELETE on the table SELECT user INTO v_username FROM dual; -- Insert record into audit table INSERT INTO orders_audit ( order_id, quantity, cost_per_item, total_cost, delete_date, deleted_by ) VALUES ( :old.order_id, :old.quantity, :old.cost_per_item, :old.total_cost, sysdate, v_username ); END;