PLSQL :NEW and :OLD

Question

Can anyone help me understand when to use :NEW and :OLD in PLSQL blocks, I\'m finding it very difficult to understand their usage.

Answer 1

:old and :new are pseudorecords referred to access row level data when using row level trigger.

• :old - refers to Old Value
• :new - refers to New value

For Below operation, respective old and new values:

1. INSERT- :old.value= NULL, :new value= post insert value
2. DELETE- :old.value= Pre Delete value, :new value= null
3. UPDATE- :old.value= Pre update value, :new value= Post Update value

Eg:

CREATE OR REPLACE TRIGGER get_dept
  BEFORE DELETE OR INSERT OR UPDATE ON employees
  FOR EACH ROW
BEGIN
    DBMS_OUTPUT.PUT('Old Dept= ' || :OLD.dept|| ', ');
  DBMS_OUTPUT.PUT('New Dept= ' || :NEW.dept );
END;

Triggering Statement:

UPDATE employees
SET dept ='Accounts'
WHERE empno IN (101 ,105);

Answer 2

New and Old more relevant for update operation inside a trigger, to fetch old value of field use old and for recent value use new

Answer 3

You normally use the terms in a trigger using :old to reference the old value and :new to reference the new value.

Here is an example from the Oracle documentation linked to above

CREATE OR REPLACE TRIGGER Print_salary_changes
  BEFORE DELETE OR INSERT OR UPDATE ON Emp_tab
  FOR EACH ROW
WHEN (new.Empno > 0)
DECLARE
    sal_diff number;
BEGIN
    sal_diff  := :new.sal  - :old.sal;
    dbms_output.put('Old salary: ' || :old.sal);
    dbms_output.put('  New salary: ' || :new.sal);
    dbms_output.put_line('  Difference ' || sal_diff);
END;

In this example the trigger fires BEFORE DELETE OR INSERT OR UPDATE :old.sal will contain the salary prior to the trigger firing and :new.sal will contain the new value.

Answer 4

You can use :OLD while working on after/before update 100% of time :NEW is a record of the new value added by (insert or update) :OLD is for old values. Without them, triggers are useless

Answer 5

:new is the new value - After the trigger is fired this is the value of the column :old is the old value - After the trigger is fired this value is replaced with :new value

Answer 6

:new means the new value your are trying to insert :old means the existing value in database