Declarative Referential Integrity

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Declarative Referential Integrity (DRI) is one of the techniques in the SQL database programming language to ensure data integrity.

Meaning in SQL

A table (called the child table) can refer to a column (or a group of columns) in another table (the parent table) by using a foreign key. The referenced column(s) in the parent table must be under a unique constraint, such as a primary key. Also, self-references are possible (not fully implemented in MS SQL Server though^[1]). On inserting a new row into the child table, the relational database management system (RDBMS) checks if the entered key value exists in the parent table. If not, no insert is possible. It is also possible to specify DRI actions on UPDATE and DELETE, such as CASCADE (forwards a change/delete in the parent table to the child tables), NO ACTION (if the specific row is referenced, changing the key is not allowed) or SET NULL / SET DEFAULT (a changed/deleted key in the parent table results in setting the child values to NULL or to the DEFAULT value if one is specified).

Product specific meaning

In Microsoft SQL Server the term DRI also applies to the assigning of permissions to users on a database object. Giving DRI permission to a database user allows them to add foreign key constraints on a table.^[2]

References

1. ^ Microsoft Support (2007-02-11). "Error message 1785 occurs when you create a FOREIGN KEY constraint that may cause multiple cascade paths". microsoft.com. http://support.microsoft.com/kb/321843/en-us. Retrieved 2009-01-24. 
2. ^ Chigrik, Alexander (2003-08-13). "Managing Users Permissions on SQL Server". Database Journal. http://www.databasejournal.com/features/mssql/article.php/2246271. Retrieved 2006-12-17. 

External links

• DRI versus Triggers