In this example, the primary key values from the Orders table of customer I.D. = 5678 and order data = 20 July 2003 are copied into three rows of the Order Lines table, where they become foreign key values. Each copy represents a different product that was ordered by the same person on the same date. One of these products is identified by UPC = 51820 33622, which is a foreign key value from the Products table. This product code is also copied into two other rows of the Order Lines table, but each of those lines represents a different order, either placed by a different customer, placed on a different date, or both.
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