storing the same information in more than one file.
E.g. a customers address stored in more than one file.
maintaining accurate data. If a customer’s address is changed will it be changed in all files? If not the data loses it’s integrity - it is inaccurate.
Example Customers Customer Number Company Name Address City, State, Phone Number Orders Order Number Order Date Order Line Items Item Number Description Quantity Price Each time an order is placed, you'll need to repeat the customer information, including the Customer Number, Company Name, etc. A company which takes orders from many customers
A foreign key represents the value of primary key for a related table.
Foreign keys are the cornerstone of relational databases.
Example In the Customers Table, the CustID field will contain the data to uniquely identify a customer. This is the primary key. In the Orders table, the OrdCustID field would hold the value of the CustID field for the customer who placed the order. This makes OrdCustID a foreign key
Solution Customers CustID CustName CustAddress CustCity CustState CustPhone Orders OrdID OrdCustID OrdDate OrderDetails ODID ODOrdID ODDescription ODQty ODPrice In the Orders table, the OrdCustID field would hold the value of the CustID field for the customer who placed the order. Primary Keys Foreign Keys