The basic premise of a relational database is that tables are related. These relationships are maintained and enforced via referential integrity.
FOREIGN KEY constraints are the declarative means for enforcing referential integrity in SQL Server. You implement
FOREIGN KEY constraints by relating one or more columns in a table to the columns in a primary key or unique index. The columns in the referencing table can be referred to as foreign key columns. The table with the primary key or unique index can be referred to as the primary table. Figure 23.2 shows a relationship between the
BusinessEntityAddress table and
AddressType table. The foreign key in this example is
AddressTypeID on the