View (SQL): Difference between revisions

Revision as of 14:39, 21 September 2022

Revision as of 19:53, 18 March 2023

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== Read-only vs. updatable views ==

Database practitionersViews can definebe viewsdefined as [[file system permissions|read-only]] or updatable. If the database system can determine the reverse mapping from the view schema to the schema of the underlying base tables, then the view is updatable. [[Insert (SQL)|INSERT]], [[Update (SQL)|UPDATE]], and [[Delete (SQL)|DELETE]] operations can be performed on updatable views. Read-only views do not support such operations because the DBMS cannot map the changes to the underlying base tables. A view update is done by key preservation.

Some systems support the definition of INSTEAD OF [[Database trigger|triggers]] on views. This technique allows the definition of other logic for execution in place of an insert, update, or delete operation on the views. Thus database systems can implement data modifications based on read-only views. However, an INSTEAD OF trigger does not change the read-only or updatable property of the view itself.