Entity Integrity Entity integrity defines a row as a unique entity for a particular table. Entity integrity enforces the integrity of the identifier column(s) or the primary key of a table (through indexes, UNIQUE constraints, PRIMARY KEY constraints, or IDENTITY properties). Domain Integrity Domain integrity validates the entries for a given column. Domain integrity can be enforced by restricting the type (through data types), the format (through CHECK constraints and rules), or the range of possible values (through FOREIGN KEY and CHECK constraints, DEFAULT definitions, NOT NULL definitions, and rules).

Referential Integrity Referential integrity maintains the defined relationship between tables when records are entered or deleted from the tables. In SQL Server 2000, referential integrity is based on relationships between foreign keys and primary keys or between foreign keys and unique keys (through FOREIGN KEY and CHECK constraints). Referential integrity ensures that key values are consistent across the related tables.When referential integrity is enforced, SQL Server prevents users from adding records to a related table if there is no associated record in the primary table. Users are also prevented from changing values in a primary table or deleting records from the primary table if there are related records in the related table. User-Defined Integrity User-defined integrity is used to define specific business rules that do not fall into any of the other integrity categories. All of the integrity categories support user-defined integrity.