Advanced Database Management System - Tutorials and Notes: Codd's Twelve Rules - Rule 6 - View Updating Rule

Wednesday, 18 February 2015

Codd's Twelve Rules - Rule 6 - View Updating Rule


Codd's Twelve Rules - Rule 6 - View Updating Rule



Rule 6
View Updating Rule
Rule
All views that are theoretically updateable are also updateable by the system.
Description
This rule deals with views, which are virtual tables used to give various users of a database different views of its structure. It’s one of the most challenging rules to implement in practice, and no commercial product fully satisfies it today. A view is theoretically updateable as long as it’s made up of columns that directly correspond to real table columns.
Example
All views are not updateable. Views can be updateable if they follow the certain rules unlike tables. The following syntax can be used to update views;
UPDATE < view_name > SET<column1>=<value1>,<column2>=<value2>,.....
WHERE <condition>;
Some DBMS that fulfills this property
  • SQL Server technically fulfills this rule by using INSTEAD OF triggers,
  • MySQL support view update in some cases. For a view to be updatable, there must be a one-to-one relationship between the rows in the view and the rows in the underlying table in MySQL,
  • All views that are theoretically updateable are also updateable by the Oracle system.


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