Referential integrity constraints (also known as foreign key constraints or referential constraints) enable you to define required relationships between and within different tables. Referential integrity is the state of a database in which all values of all foreign keys are valid. A foreign key is a column or a set of columns in a table whose values are required to match at least one primary key or unique key value of a row in its parent table.
To understand how referential constraints work, let's establish a relationship between the EMPLOYEE and DEPARTMENT tables, as shown in the following diagram. In this example, a single column DEPTID defines the parent key and the foreign key of the referential constraint. ...
