A primary key

Full Answer Section Natural keys are most commonly used in business information processing because they are easy to understand and use. However, natural keys are not always available, and in some cases, an invented key may be needed. What is a foreign key? Why are foreign keys used or required in a relational database? Are duplicate foreign key values allowed? Why or why not? A foreign key is a field or group of fields in a database table that refers to the primary key of another table. Foreign keys are used to establish relationships between tables in a relational database. For example, a customer table might have a foreign key that refers to the primary key of an order table. This would allow us to see which customers have placed orders. Foreign keys are required in a relational database because they help to maintain the integrity of the data. If a record is deleted from the table that contains the primary key, the foreign key in the other table will be set to NULL. This prevents the foreign key from referencing a record that no longer exists. Duplicate foreign key values are not allowed because they would violate the referential integrity constraint of the foreign key. The referential integrity constraint ensures that the foreign key value in one table always refers to a valid primary key value in the other table.

Sample Answer What is a primary key? Are duplicate primary keys allowed? Why or why not? A primary key is a field or group of fields in a database table that uniquely identifies each record in the table. Duplicate primary keys are not allowed because they would violate the uniqueness constraint of the primary key. The primary key is used to identify a particular record in a table, and if there were two records with the same primary key value, it would be impossible to tell which record was which. What is the difference between a natural key and an invented key? Which type is most commonly used in business information processing? A natural key is a field or group of fields that naturally identifies a record in a table. For example, the customer ID field in a customer table would be a natural key because it uniquely identifies each customer in the table. An invented key is a field or group of fields that is not naturally associated with a record in a table, but is used to uniquely identify the record. For example, a randomly generated number could be used as an invented key.