Foreign Keys v12
Suppose you want to make sure all employees belong to a valid department. This is called maintaining the referential integrity of your data. In simplistic database systems this would be implemented (if at all) by first looking at the
dept table to check if a matching record exists, and then inserting or rejecting the new employee record. This approach has a number of problems and is very inconvenient. Advanced Server can make it easier for you.
A modified version of the
emp table presented in Creating a New Table is shown in this section with the addition of a foreign key constraint. The modified
emp table looks like the following:
If an attempt is made to issue the following
INSERT command in the sample
emp table, the foreign key constraint,
emp_ref_dept_fk, ensures that department
50 exists in the
dept table. Since it does not, the command is rejected.
The behavior of foreign keys can be finely tuned to your application. Making correct use of foreign keys will definitely improve the quality of your database applications, so you are strongly encouraged to learn more about them.