Lesson Review in VS .NET

Drawing PDF-417 2d barcode in VS .NET Lesson Review

Lesson Review
Draw PDF417 In .NET
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Reading PDF417 In .NET
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The following questions are intended to reinforce key information presented in this lesson. The questions are also available on the companion CD if you prefer to review them in electronic form.
Barcode Encoder In .NET
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Scanning Bar Code In Visual Studio .NET
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NOTE
PDF417 Printer In Visual C#
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PDF417 Generator In .NET
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Answers
Encoding PDF 417 In Visual Basic .NET
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UPC-A Supplement 5 Creator In VS .NET
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Answers to these questions and explanations of why each answer choice is right or wrong are located in the Answers section at the end of the book.
Making Barcode In .NET Framework
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Generate EAN / UCC - 14 In Visual Studio .NET
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1. Which of the following options can prevent a table from being dropped A. CHECK OPTION B. SCHEMABINDING C. UNION D. QUOTED_IDENTIFIER
Draw Data Matrix In .NET
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Creating British Royal Mail 4-State Customer Code In VS .NET
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Lesson 2: Modifying Data Through Views
QR Code 2d Barcode Printer In None
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Making DataMatrix In Java
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Lesson 2: Modifying Data Through Views
Draw Code 128C In None
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Decoding Barcode In None
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As noted previously, a view is just a named SELECT statement. In effect, a view is a pass-through reference to one or more base tables. Although most views provide read access to underlying data, because a view is a pass-through you can also make data modifications through it. A view that enables you to modify data is called an updateable view. This lesson explains how you can perform INSERT, UPDATE, DELETE, BCP, and BULK INSERT operations against a view.
UPCA Recognizer In Visual C#.NET
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Decoding Data Matrix In Java
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After this lesson, you will be able to:
Code 39 Full ASCII Creation In Objective-C
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QR Code JIS X 0510 Encoder In None
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Create an updateable view.
Estimated lesson time: 20 minutes
Creating Updateable Views
Although you can define a view based on more than one table, SQL Server restricts any data modifications you execute through the view to a single table. In addition, all changes must directly reference columns and not derivations of a column. Thus, you cannot modify columns that are derived through an aggregate function, such as AVG, COUNT, SUM, MIN, or MAX, or through a computation that involves other columns or operations on a column, such as SUBSTRING. Changes cannot reference columns generated by using operators such as UNION, CROSSJOIN, and INTERSECT. In addition, the view definition cannot contain a GROUP BY, HAVING, or DISTINCT clause. And you cannot use TOP when you specify WITH CHECK OPTION.
BEST PRACTICES
Using views to modify data
Although you can use views to insert, update, and delete data, views are almost never used for that purpose. Stored procedures are always a better option because you can more easily validate changes via stored procedures. Stored procedures are also more flexible.
In your view definition, you can include a WHERE clause that limits the range of rows that the view returns. However, the WHERE clause does not restrict the changes that users can make through the view. To restrict the changes that users can make, you use the CREATE VIEW command s WITH CHECK OPTION clause when defining the view. Let s look at a brief example to see how the CHECK OPTION clause works. Suppose that you define a view that shows customers who have a credit line greater than $1,000. A user could insert a new customer who has a credit line of $500 and not cause an error. However, doing so could cause confusion because although the insert
7
Implementing Views
was successful, the view cannot display the inserted data, and a user might think that the data had been lost. So to restrict the changes that users can make so that the data is always visible through the view, you should define the view by using the WITH CHECK OPTION clause. If you define the preceding view with the CHECK OPTION clause, a user s attempt to insert a customer with a credit line of $1,000 or less causes an error to be returned. You can also create triggers on a view, which are useful for performing data-modification operations. You create a special kind of trigger on views called an INSTEAD OF trigger. INSTEAD OF triggers operate exactly as you would expect: Instead of SQL Server performing the operation against the view, SQL Server executes the trigger to perform an alternative operation.
MORE INFO
INSTEAD OF triggers
For more information about triggers, see 9, Creating Functions, Stored Procedures, and Triggers.
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