SQL视图与编程：功能、应用与实践

### SQL视图与编程：功能、应用与实践 #### 引言 在数据库管理中，SQL视图是一项非常强大的工具，它可以帮助我们简化操作、隐藏敏感信息、优化查询结果等。同时，将SQL语句嵌入程序代码以及使用SQL用户定义函数也能极大地提升开发效率和代码的可维护性。下面我们将详细介绍SQL视图的各种用途、如何更新视图、如何将SQL嵌入程序代码以及SQL用户定义函数的使用。 #### SQL视图的用途 SQL视图具有多种用途，以下是一些常见的应用场景： 1. **隐藏列和行** - **隐藏列**：可以使用SQL视图隐藏某些列，以简化结果或防止敏感数据的显示。例如，若View Ridge Gallery的用户需要一个仅包含客户姓名和电话号码的简化列表，可以定义如下视图： ```sql /* *** SQL-CREATE-VIEW-CH07-02 *** */ CREATE VIEW CustomerBasicDataView AS SELECT LastName AS CustomerLastName, FirstName AS CustomerFirstName, AreaCode, PhoneNumber FROM CUSTOMER; ``` 要使用这个视图，可以运行以下SQL语句： ```sql /* *** SQL-Query-View-CH07-02 *** */ SELECT * FROM CustomerBasicDataView ORDER BY CustomerLastName, CustomerFirstName; ``` - **隐藏行**：通过在视图定义中提供`WHERE`子句，可以隐藏某些行。例如，定义一个仅包含华盛顿州客户姓名和电话数据的视图： ```sql /* *** SQL-CREATE-VIEW-CH07-03 *** */ CREATE VIEW CustomerBasicDataWAView AS SELECT LastName AS CustomerLastName, FirstName AS CustomerFirstName, AreaCode, PhoneNumber FROM CUSTOMER WHERE State='WA'; ``` 使用该视图的SQL语句如下： ```sql /* *** SQL-Query-View-CH07-03 *** */ SELECT * FROM CustomerBasicDataWAView ORDER BY CustomerLastName, CustomerFirstName; ``` 2. **显示计算列的结果** 视图的另一个用途是显示计算列的结果，而无需用户输入计算表达式。例如，将`AreaCode`和`PhoneNumber`列组合并格式化结果： ```sql /* *** SQL-CREATE-VIEW-CH07-04 *** */ CREATE VIEW CustomerPhoneView AS SELECT LastName AS CustomerLastName, FirstName AS CustomerFirstName, ('(' + AreaCode + ') ' + PhoneNumber) AS CustomerPhone FROM CUSTOMER; ``` 执行以下SQL语句查看结果： ```sql /* *** SQL-Query-View-CH07-04 *** */ SELECT * FROM CustomerPhoneView ORDER BY CustomerLastName, CustomerFirstName; ``` 将计算放在视图中有两个主要优点：一是节省用户编写表达式的时间和精力；二是确保结果的一致性。 3. **隐藏复杂的SQL语法** 使用视图可以隐藏复杂的SQL语法，开发者在需要特定结果时无需输入复杂的SQL语句。例如，View Ridge Gallery的销售人员想查看哪些客户对哪些艺术家感兴趣，并显示客户和艺术家的姓名，需要进行两次连接操作。可以定义如下视图： ```sql /* *** SQL-CREATE-VIEW-CH07-05 *** */ CREATE VIEW CustomerInterestsView AS SELECT C.LastName AS CustomerLastName, C.FirstName AS CustomerFirstName, A.LastName AS ArtistName FROM CUSTOMER AS C JOIN CUSTOMER_ARTIST_INT AS CAI ON C.CustomerID = CAI.CustomerID JOIN ARTIST AS A ON CAI.ArtistID = A.ArtistID; ``` 使用该视图的SQL语句如下： ```sql /* *** SQL-Query-View-CH07-05 *** */ SELECT * FROM CustomerInterestsView ORDER BY CustomerLastName, CustomerFirstName; ``` 4. **分层内置函数** 可以构建一个计算变量的视图，然后在该视图的SQL语句中使用计算变量的`WHERE`子句。例如，定义`ArtistWorkNetView`视图： ```sql /* *** SQL-CREATE-VIEW-CH07-06 *** */ CREATE VIEW ArtistWorkNetView AS SELECT LastName AS ArtistLastName, FirstName AS ArtistFirstName, W.WorkID, Title, Copy, DateSold, AcquisitionPrice, SalesPrice, (SalesPrice – AcquisitionPrice) AS NetProfit FROM TRANS AS T JOIN WORK AS W ON T.WorkID = W.WorkID JOIN ARTIST AS A ON W.ArtistID = A.ArtistID; ``` 使用`NetProfit`的`WHERE`子句查询： ```sql /* *** SQL-Query-View-CH07-06 *** */ SELECT ArtistLastName, ArtistFirstName, WorkID, Title, Copy, DateSold, NetProfit FROM ArtistWorkNe ```