Referential Integrity in SQL

1. An addition to the original standard allows specification of primary and candidate keys and foreign keys as part of the create table command:
   • primary key clause includes a list of attributes forming the primary key.
   • unique key clause includes a list of attributes forming a candidate key.

   • foreign key clause includes a list of attributes forming the foreign key, and the name of the relation referenced by the foreign key.
2. An example illustrates several features mentioned so far: