单选题 You are the administrator of a SQL Server 2000 computer. The server contains a database named Inventory. Users report that several storage locations in the UnitsStored field contain negative numbers. You examine the database's table structure. The table properties are configured as shown in the exhibit.

A、 ALTER TABLE dbo.storagelocations ADD CONSTRAINTS CK_storagelocations_UnitsStored CHECK (UnitsStored>= 0)
B、 CREATE TRIGGER CK_UnitsStored On StorageLocations FOR INSERT, UPDATE AS IF INSERTED, UnitsStored < 0 ROLLBACK TRAN
C、 CREATE TABLE ck_unitsstored As @Units >= 0 GO Sp_bindrule ‘OK_UnitsStored’, ‘StorageLocations, UnitsStored’ GO
D、 CREATE PROC UpdateUnitsStored (StorageLocationID int, @UnitsStored bigint)AS IF @UnitsStored < 0 DATSERROR (50099, 17) ELSE UPDATE storaheLocations SET UnitsStored = @UnitsStored WHERE StorageLocationID = @storageLocationID

【正确答案】 A

【答案解析】解析：Explanation: CHECK constraints are used to enforce domain integrity by restricting the values that are accepted by a column. They determine which values are valid by testing a logical expression that is not based on data in another column. The problem posed by this scenario can be solved through the implementation of such a constraint. In this solution the CHECK constraint is added in line 1 and the CHECK expression is specified in line 3. The expression specifies that the values contained in the UnitsStored column must be more than or equal to 0. Incorrect Answers: B: This solution uses a trigger to perform the CHECK constraint, which a trigger can do. However, it is recommended that triggers only be used when the CHECK constraint cannot meet the functionality required by the application. This is thus not the best answer. C: In this solution creates a new table is created with the CREATE TABLE statement. This is inappropriate to the problem, as it does not address the insertion of negative values in the existing table. D: This solution creates a stored procedure to perform the CHECK constraint.