Editing Referential integrity (section)

==Declarative referential integrity==
'''Declarative referential integrity''' (DRI) is one of the techniques in the [[SQL]] database programming language to ensure data integrity.

===Meaning in SQL=== 
{{main|Foreign key}}
A table (called the referencing table) can refer to a column (or a group of columns) in another table (the referenced  table) by using a [[foreign key]]. The referenced column(s) in the referenced 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<ref>{{cite web |author=Microsoft Support |date=2007-02-11 |title=Error message 1785 occurs when you create a FOREIGN KEY constraint that may cause multiple cascade paths |publisher=microsoft.com |url=http://support.microsoft.com/kb/321843/en-us |access-date=2009-01-24}}</ref>). On [[Insert (SQL)|inserting]] a new [[Row (database)|row]] into the referencing table, the [[relational database management system]] (RDBMS) checks if the entered key value exists in the referenced table. If not, no insert is possible. It is also possible to specify DRI actions on [[Update (SQL)|UPDATE]] and [[Delete (SQL)|DELETE]], such as CASCADE (forwards a change/delete in the referenced table to the referencing 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 referenced table results in setting the referencing values to NULL or to the DEFAULT value if one is specified).<ref>
ANSI/ISO/IEC 9075-1:2003, Information technology—Database languages—SQL
* Part 1: Framework (SQL/Framework)
* Part 2: Foundation (SQL/Foundation)
</ref>

===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.<ref>{{cite web |last=Chigrik |first=Alexander |date=2003-08-13 |title=Managing Users Permissions on SQL Server |publisher=Database Journal |url=http://www.databasejournal.com/features/mssql/article.php/2246271 |access-date=2006-12-17}}</ref>