Process: - When user buy item and check out then there's cart and cart items table to store the transaction.
              - 1 cart_id have many item which stored in cart items table.
              - After purchase succeed, then will generate a purchase order id and stored in purchase order table .
              - In purchase order table, id_cart and status will be stored.

From  here, i am trying to calculate quantity based on id_product or id branch or etc from the purchase made.
There is receiving and ordered quantity field, which in some cases quantity received field might be null, so i will take ordered quantity value.

cart item table

cart table

purchase order table