Editing Referential integrity (section)

===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)
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