Beginning SQL

However, someone writes a query that mistakenly inserts a member in another state:
INSERT INTO MemberBirthdaysGoldenState
(MemberId, LastName, FirstName, DateOfBirth, Street, City,
State, ZipCode, Email, DateOfJoining)
VALUES (7, ‘Smith’, ‘Marty’, ‘3/23/1974’, ‘123 North Rd’, ‘Idlewild’, ‘New
State’, 65421, ‘msmith@SmithSonJonSon.com’, ‘3/01/2004’)
This is a perfectly valid SQL statement, however, and the query inserts a new record into the
MemberDetails table in a state that is not visible in the view, and which does not belong to the user
doing the update. This user cannot see the new record and thinks that the DBMS ignored his request,
and some other user now finds a record in his state for a member he didn’t add.
In order to prevent this kind of problem, you might want to disallow these updates from occurring
through the view. The DBMS can do this for you using the CHECK OPTION keyword in the CREATE VIEW
statement, as shown below in the new version of the view:
CREATE VIEW MemberBirthdaysGoldenStateCheckOption AS
SELECT MemberId, FirstName, LastName, DateOfBirth, Street, City, State,
ZipCode, Email, DateOfJoining
FROM dbo.MemberDetails
WHERE (State = ‘Golden State’)
WITH CHECK OPTION
When you specify the CHECK OPTION keyword in a CREATE VIEW statement, the DBMS stores the
CHECK OPTION with the view. Whenever a user performs an UPDATE, INSERT, or DELETE on the view,
the DBMS checks each operation to ensure that it meets the WHERE criteria. Any operations failing to
meet the WHERE criteria are not performed. For example, an attempt to execute the following statement
would fail:
INSERT INTO MemberBirthdaysGoldenStateCheckOption
(MemberId, LastName, FirstName, DateOfBirth, Street, City, State, ZipCode,
Email, DateOfJoining)
VALUES
(7, ‘Smith’, ‘Marty’, ‘3/23/1974’, ‘123 North Rd’, ‘Idlewild’, ‘New State’,
65421,
‘msmith@SmithSonJonSon.com’, ‘3/01/2004’)
You would see results similar to Figure 10-12.
Figure 10-12
Views
As you might imagine, CHECK OPTION can add significant overhead to an action query. Each record
being updated has to be checked for conformance with the view. Additionally, you can build views
based on other views, and each may have a CHECK OPTION. Each level must be checked to ensure that
the requested operation passes its check.
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