Integrity constraints

Data stored in the database must adhere to certain business rules. An integrity constraint defines a business rule for a table column. When the integrity constraint is enabled, Oracle will enforce the business rule. Integrity constraints are stored as part of table definition within the database.

The following are the integrity constraints:

• NOT NULL: The NOT NULL constraint enforces a column to not accept null values.

• CHECK: The CHECK constraint is used to limit the values that are accepted by a column.

• UNIQUE: The UNIQUE constraint is used to make sure that no duplicate values are entered in the column.

• PRIMARY KEY: The PRIMARY KEY constraint is used to uniquely identify a row in a table. PRIMARY KEY can be thought of as a combination of the UNIQUE key and NOT NULL constraints. Furthermore, a table can have only one primary key.

• FOREIGN KEY: A foreign key column is used to establish link between two tables. The FOREIGN KEY constraint on a column ensures that the...