What is Referential Integrity

Building and maintaining logical relationships between tables are fundamental parts of working with relational databases. Most databases must maintain certain relationships or the data will be logically corrupt. When such relationships exist, we say that the data has referential integrity. One table is the referenced table and the other is the referencing table; values in the referencing table must match values in the referenced table. (Some people call these tables parent and child tables, but that terminology implies a hierarchy, which the relational model avoids.) SQL Server can automatically enforce referential integrity through foreign key constraints that you define. This feature is called Declarative Referential Integrity (DRI) because it's part of the table definition. You can also use other features, such as triggers, to enforce relationships; this use is procedural referential integrity.