Oracle view what is

Python Design Patterns. Python Pillow. Python Turtle. Verbal Ability. Interview Questions. Company Questions. Artificial Intelligence. Cloud Computing. Data Science. Angular 7. No special privileges are required to query these views. Dynamic performance views monitor ongoing database activity.

They are available only to administrators. Oracle Database Concepts. For a view to be inherently updatable, the following conditions must be met:. Each column in the view must map to a column of a single table. For example, if a view column maps to the output of a TABLE clause an unnested collection , then the view is not inherently updatable. In addition, if an inherently updatable view contains pseudocolumns or expressions, then you cannot update base table rows with an UPDATE statement that refers to any of these pseudocolumns or expressions.

If you want a join view to be updatable, then all of the following conditions must be true:. A key-preserved table is one for which every primary key or unique key value in the base table is also unique in the join view. Oracle Database Administrator's Guide for more information on updatable views. Oracle Database Application Developer's Guide - Fundamentals for more information about updating object views or relational views that support object types.

There is a subquery within the defining query of this view or any view on which this view is based or. The view shows the employees in department 20 and their annual salary:. Creating a View with Constraints: Example The following statement creates a restricted view of the sample table hr. Creating an Updatable View: Example The following statement creates an updatable view named clerk of all clerks in the employees table.

Only the employees' IDs, last names, department numbers, and jobs are visible in this view, and these columns can be updated only in rows where the employee is a kind of clerk:. You cannot subsequently insert a new row into clerk if the new employee is not a clerk. Creating a Join View: Example A join view is one whose view subquery contains a join.

If at least one column in the join has a unique index, then it may be possible to modify one base table in a join view. For example:. A view takes the output of a query and makes it appear like a virtual table. You can use a view in most places where a table can be used. All operations performed on a view will affect data in the base table and so are subject to the integrity constraints and triggers of the base table.

A View can be used to simplify SQL statements for the user or to isolate an application from any future change to the base table definition.

A View can also be used to improve security by restricting access to a predetermined set of rows or columns.