A view is basically a logical view of one or more base tables. A view can be a read only or Updatable. A view generally be Created to avoid any unwanted changes into actual base tables. Mainly view is created for security reasons.
- A view can be constructed with another view so it is called as nested view.
- You can create or replace an existing view
- A view can be created without having base tables. This is possible with FORCE option.
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Read only views: The standard syntax for view is as follows:
CREATE OR REPLACE VIEW INVOICE_SUMMARY AS
COUNT(*) AS INVOICE_COUNT,
SUM(INVOICE_TOTAL) AS INVOICE_TOTAL_SUM
JOIN INVOICES ON VENDORS.VENDOR_ID*INVOICES.VENDOR_ID
GROUP BY VENDOR_NAME;
How to use FORCE command:
CREATE FORCE VIEW PRODUCTS_LIST AS
SELECT PRODUCT_DESCRIPTION, PRODUCT_PRICE
Updatable Views: A view can also be updatable if a view follows certain rules. Read more to understand all about what is updatable view.
- A view when it is created for update purpose, you can give INSERT,UPDATE and DELETE
- A read only view should contain WITH READ ONLY CLAUSE.
While updating a view, it is possible to update only one base table at a time. When you created a view from more than one table, then it is not possible to update two tables at a time.
What is ALTER view
This is possible with CREATE OR REPLACE statement. Just you can replace with existing statement.
DROP VIEW VENDORS_SW
Last pointsA view with CHECK OPTION is surely help you to satisfy certain condition. Usually this option will be used in updatable views.