11. Also, foreign keys are not supported. 12. PostgreSQL is triggers, foreign keys ; supports functions and stored procedures, and other expandability. 13. In Relational database terms, the ReportsTo column is a foreign key referencing the EmpNo column. 14. File cross-connects or joins are handled as a synonym definition of the foreign key . 15. Each foreign key constraint is dependent upon a unique database index from the parent database table. 16. When a PK migrates to another table, it becomes a foreign key in the other table. 17. In particular, natural join allows the combination of relations that are associated by a foreign key . 18. Database tables in a cache group must each have a defined primary key-foreign key constraints. 19. It is also used to decide in which order to load tables with foreign keys in databases. 20. For Sqlite2 and MySQL 5.1 . x it provides automatic relation discovery through foreign keys .
