CHECK Option

The WITH CHECK OPTION is a clause in SQL that you can add at the end of a CREATE VIEW or ALTER VIEW statement. It ensures that all UPDATE and INSERT operations performed on the view must result in rows that meet the conditions of the view definition. If an UPDATE or INSERT operation would result in rows that do not meet the view's conditions, the DBMS returns an error and does not perform the operation.

Here's an example:

CREATE VIEW Top_Customers AS
SELECT CustomerName, ContactName 
FROM Customers
WHERE Orders > 50
WITH CHECK OPTION;

In this example, if you tried to UPDATE or INSERT a row through the Top_Customers view where the number of orders is not more than 50, you would get an error.

The WITH CHECK OPTION is useful to maintain data integrity in views that are used for data insertion or modification. It ensures that only data that fits the criteria of the view can be inserted or modified through the view.

Also note that, if you're using a WITH CHECK OPTION on a view that is based on another view, you can specify the CASCADED keyword before the CHECK OPTION. This ensures that the conditions of all underlying views are checked when you perform an UPDATE or INSERT operation. If you do not specify CASCADED, only the immediate view's conditions are checked, which is the LOCAL check option. If neither CASCADED or LOCAL are specified, the default is CASCADED.