Trigger compilation errors in 11g

Question

Using 11g Win 2008 Server 64 bit. I'm trying to create a trigger that willl automatically calculate the total cost of an item from the quantity required multiplied by unit cost. The trigger is used to overide user input if the toal cost of an item is left blank. I've tried variations to the following syntax and would appreciate advice on the right syntax to use. Many thanks, J
CREATE OR REPLACE TRIGGER prodreq_qtycalc
AFTER INSERT ON PRODUCT_REQUIREMENTS
FOR EACH ROW
BEGIN
IF :OLD.TOTALCOST IS NULL
THEN UPDATE PRODUCT_REQUIREMENTS
SET :NEW.TOTALCOST = (UNITCOST * QTYNEEDED);
END;

Answer 1

Jay wrote:
Using 11g Win 2008 Server 64 bit. I'm trying to create a trigger that willl automatically calculate the total cost of an item from the quantity required multiplied by unit cost. The trigger is used to overide user input if the toal cost of an item is left blank. I've tried variations to the following syntax and would appreciate advice on the right syntax to use. Many thanks, J
CREATE OR REPLACE TRIGGER prodreq_qtycalc
AFTER INSERT ON PRODUCT_REQUIREMENTS
FOR EACH ROW
BEGIN
IF :OLD.TOTALCOST IS NULL
THEN UPDATE PRODUCT_REQUIREMENTS
SET :NEW.TOTALCOST = (UNITCOST * QTYNEEDED);
END;As a general rule it is a BAD design to store computed value in row.
what if either UNITCOST or QTYNEEDED is NULL?
  1  CREATE OR replace TRIGGER prodreq_qtycalc
  2    before INSERT ON product_requirements
  3    FOR each ROW
  4    WHEN (old.totalcost IS NULL)
  5  DECLARE
  6  BEGIN
  7      :NEW.totalcost := ( :old.unitcost * :old.qtyneeded );
  8* END prodreq_qtycalc;
SQL> /
Trigger created.