PLSQL Code for Substracting / Reducing Quantity

Question

Hi All
I have two tables Cash and Product. Cash table has cash related sales in it. Product has product information in it.
End user selects the products and specifying their quantity in cash form then saves it. The quantity must be reduced or deducted form product table before the next cash sale is booked in cash so it will reflect the actual stock or quantity of product.
My question is how to know the end user has selected which product and it's quantity?
What would be the code?
Best Regards
Thunder2777

Answer 1

Hi,
If you don't already have one, add a quantity_in_stock column to the product table, with a check constraint that guarantees this column is greater than or equal to 0.
Add a trigger to the cash table, to change product.quantity_in_stock when any change is made to the cash table, somehting like this untested example:
CREATE OR REPLACE TRIGGER     cash_bdiu
BEFORE     DELETE OR INSERT OR UPDATE
ON     cash
FOR EACH ROW
DECLARE
     net_amt     NUMBER     := NVL (:NEW.quantity;, 0);
BEGIN
     IF  :OLD.quantity != 0
     THEN     -- Add back old quantity
          IF  :OLD.product != :NEW.product
          THEN     -- undo previous transaction
               UPDATE  procuct
               SET     quantity_in_stock := quantity_in_stock + :OLD.quantity
               WHERE     product_id       = :OLD.product_id;
          ELSE     -- combine with normal update below
               net_amt := net_amt - :OLD.quantity;
          END IF;
     END IF;
     IF  net_amt != 0
     THEN
          UPDATE  product
          SET     quantity_in_stock := quantity_in_stock - net_quantity
          WHERE     product_id       = :NEW.product_id;
     END IF;
END;Most of the complexity is due to handling situation like:
(a) a row is deleted
(b) a row is updated with a different quantity
(c) a row is updated with a different product_id (and perhaps a different quantity)
We want to avoid doing two UPDATES on the same row of product in the same call to this trigger. That's why I used the local variable net_amount.