In the Linked Item table, you can link retail items together, then every time the main retail item is sold,
the retail items that are linked to it are sold as well. The Linked Item table contains information about which items are linked and the item quantity that
is linked.
You can use linking for example when selling drinks in glass bottles. The bottles are then linked to the drink so that every time the drink is sold,
the bottle is sold with it. You can also use linking like a bill of material. For example, when selling a bed, you can link the mattress,
frame and legs to the bed item, so that each time the bed is sold (bearing zero price),
the other items are sold automatically.
It is important to make a distinction between the main item and the linked item.
Each time the main item is sold, the item that is linked to it, is sold as well. The reverse does not apply,
that is, when the linked item is sold, the main item is not sold as well. The main item cannot be linked to other items, that is,
it can never appear as a linked item. Neither can you link an item to itself.