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  3. You are the administrator of a SQL Server 2000 computer. The server contains a database named sales. You need to change the way

You are the administrator of a SQL Server 2000 computer. The server contains a database named sales. You need to change the way

admin2009-05-19  35
问题 You are the administrator of a SQL Server 2000 computer. The server contains a database named sales. You need to change the way customer Ids appear in the Customers table. The database schema is shown in the exhibit.


You need to automate the process of updating the primary key tools. You also want to minimize records locks and administration within the database during the update process.
What should you do?
选项 A、Add an ON UPDATE CASCADE constraint to the CustomerID field in the Customers table. Modify the values in the CustomerID field in the Customers table.
B、Create a duplicate record that has a new CustomerID value. Update the foreign key fields in the invoices, contacts, and quotes tables with the new value.
C、Disable the FOREIGN KEY constraints. Within a transaction, modify the values in the CustomerID field in the Customers table and all related foreign key values in the invoices, contacts, and quotes tables. Re-enable the FOREIGN KEY constraints after the keys are changed.
D、Create a Data Transformation Services package. Use the package to transform the CustomerID value and the values of the related foreign keys in the invoices, contacts, and quotes tables.
答案A
解析 Explanation: A cascading referential integrity constraints allows for the automatic updating of primary key tools by defining the actions SQL Server 2000 takes when a user deletes or updates a key to which existing foreign keys point.

The ON UPDATE CASCADE option specifies that if an attempt is made to update a key value in a row, where the key value is referenced by foreign keys in existing rows in other tables, all of the foreign key values are also updated to the new value specified for the key. If cascading referential actions have also been defined on the target tables, the specified cascading actions are also taken for the key values updated in those tables.

Incorrect Answers:
B: In this solution the FOREIGN KEY fields are updated manually.

C: Constraints allow you to define the way SQL Server 2000 enforces the integrity of a database. Constraints define rules regarding the values allowed in columns and are the standard mechanism for enforcing integrity. Using constraints is preferred to using triggers, rules, and defaults.

A FOREIGN KEY is a column or a combination of columns used to establish and enforce a link between the data in two tables and are used in conjunction with the primary keys on a referenced table. It can be used together with cascading referential constraints to automate the process of the updating primary keys. Disabling the foreign keys and re-enabling them after the data has been changed will not allow for the automation of the primary key tools. Running the whole update process within a transaction would lock the table.

D: Data Transformation Services is a set of graphical tools and programmable objects that allows for the extraction, transformation, and consolidation of data from disparate sources into single or multiple destinations.
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