Implementing Views in VS .NET

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Implementing Views
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For example, consider the following code:
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CREATE VIEW v_CustomerAddress AS SELECT a.CustomerID, a.CustomerName, c.AddressLine1, c.AddressLine2, c.AddressLine3, c.City, d.StateProvince, c.PostalCode, e.Country FROM dbo.Customer a INNER JOIN dbo.CustomerToCustomerAddress b ON a.CustomerID = b.CustomerID INNER JOIN dbo.CustomerAddress c ON b.CustomerAddressID = c.CustomerAddressID INNER JOIN dbo.StateProvince d ON c.StateProvinceID = d.StateProvinceID INNER JOIN dbo.Country e ON c.CountryID = e.CountryID; SELECT a.CustomerName, b.CreditLine FROM v_CustomerAddress a INNER JOIN dbo.Customer b ON a.CustomerID = b.CustomerID;
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The optimizer would locate the reference to the v_CustomerAddress view and substitute the view definition, rewriting the submitted query into a query similar to the following:
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SELECT a.CustomerName, f.CreditLine FROM dbo.Customer a INNER JOIN dbo.CustomerToCustomerAddress b ON a.CustomerID = b.CustomerID INNER JOIN dbo.CustomerAddress c ON b.CustomerAddressID = c.CustomerAddressID INNER JOIN dbo.StateProvince d ON c.StateProvinceID = d.StateProvinceID INNER JOIN dbo.Country e ON c.CountryID = e.CountryID INNER JOIN dbo.Customer f ON a.CustomerID = f.CustomerID;
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Understanding Ownership Chains
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Because a view references other objects, there is the potential for permission issues. Consider the objects and object owners that the diagram in Figure 7-1 shows.
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V_CustomerAddress owned by UserA
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Customer owned by UserB
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CustomerAddress owned by UserC
Figure 7-1
Defining an ownership chain
Let s say that UserA grants SELECT permission to UserD on the v_CustomerAddress view. Even though UserD has permission to execute a SELECT statement against the view, this user would receive an error when he attempts to use the view because the view is defined against the Customer and CustomerAddress tables, which are owned by a different user than either UserA or UserD. When the ownership across a chain of
Lesson 1: Creating a View
dependent objects causes an error due to insufficient permissions, you have a broken ownership chain. For UserD to be able to execute a SELECT statement against the v_CustomerAddress view, the following has to occur:
UserA grants UserD SELECT permission to the view. UserB grants UserD SELECT permission to dbo.Customer. UserC grants UserD SELECT permission to dbo.CustomerAddress.
Ownership chains
MORE INFO
For more information about ownership chains, see the SQL Server 2005 Books Online topic Ownership Chains. SQL Server 2005 Books Online is installed as part of SQL Server 2005. Updates for SQL Server 2005 Books Online are available for download at www.microsoft.com/technet/prodtechnol/sql/ 2005/downloads/books.mspx.
Quick Check
What are the restrictions on the SELECT statement within a view COMPUTE or COMPUTE BY clauses are not allowed. You cannot use the INTO keyword or OPTION clause. Temporary tables and table variables cannot be referenced. An ORDER BY clause cannot be specified unless the TOP operator is also used.
Quick Check Answer
PRACTICE
Create a View
In this practice, you use the database that contains the tables you created in 3, Creating Tables, Constraints, and User-Defined Types, to create a view to return customer information for customers who live in Canada. 1. Launch SQL Server Management Studio (SSMS), connect to your instance, open a new query window, and change context to the database containing the tables you created in 3. 2. Create a view to return information for customers who live in Canada by executing the following statement:
CREATE VIEW v_CanadaCustomerAddress AS SELECT a.CustomerID, a.CustomerName, c.AddressLine1, c.AddressLine2, c.AddressLine3, c.City, d.StateProvince, c.PostalCode, e.Country
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Implementing Views
FROM dbo.Customer a INNER JOIN dbo.CustomerToCustomerAddress b ON a.CustomerID = b.CustomerID INNER JOIN dbo.CustomerAddress c ON b.CustomerAddressID = c.CustomerAddressID INNER JOIN dbo.StateProvince d ON c.StateProvinceID = d.StateProvinceID INNER JOIN dbo.Country e ON c.CountryID = e.CountryID WHERE e.Country = 'Canada' AND PrimaryAddressFlag = 1;
3. Construct a SELECT statement to verify that the view returns only customers from Canada.
Lesson Summary
A view is simply a SELECT statement that you name and store in SQL Server as a sort of virtual table that lets you give users access to just a subset of data and that lets you improve performance, especially for complex queries. After it s defined, the view can be referenced in a SELECT statement just like a table, although it does not contain any data. When granting permissions to a view, you must pay careful attention to the ownership chain to ensure that the user has access to the view as well as all underlying objects that the view is built on.
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