Lesson 2: Formatting Result Sets in Visual Studio .NET

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Lesson 2: Formatting Result Sets
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Lesson Summary
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Use system functions and UDFs to format your data for more useful query output. UDTs can expose methods and properties to make data formatting much easier. Use column aliases to provide better column names for your data consumers.
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Lesson Review
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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.
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NOTE
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Answers
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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 this book.
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1. Which of the following functions can you use to convert integers into strings (Choose all that apply.) A. STR B. STUFF C. CAST D. CONVERT 2. Which of the following methods is exposed by all CLR UDTs for returning the UDT data as a string A. GetString B. ConvertString C. ToString D. MakeString 3. Which keyword is used to create a column alias A. STR B. AS C. FROM D. COLUMN
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5
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Working with Transact-SQL
Lesson 3: Modifying Data
In addition to knowing how to select and format data, database developers need to understand how to modify the data in the database. In this lesson, you will learn some of the best practices to consider when writing data-modification code so that you can create efficient, maintainable queries.
After this lesson, you will be able to:
Understand cursors. Create local and global temporary tables. Use the SELECT INTO command.
Estimated lesson time: 20 minutes
Understanding Cursors
One of the most important foundations of quality Transact-SQL programming is an understanding of how to think in terms of sets instead of procedurally. In almost every case, data access inside of SQL Server can be performed using set-based techniques that is, using standard SELECT statements. Even when working with very complex formatting requirements, this holds true. However, you can develop nonset-based SQL Server code by using cursors. Cursors operate by iterating through a data set one row at a time, letting the developer operate on individual rows rather than on sets of data. SQL Server supports three types of cursors: static, keyset, and dynamic. Each uses more resources than the last to detect changes to the data being queried. Static cursors use few resources because they do not detect any changes during processing. Keyset cursors detect some changes and, therefore, use more resources. Dynamic cursors detect all changes to the underlying data and are the most resource-intensive. SQL Server s query optimizer cannot generate query plans for cursors, so they are often much slower than set-based queries. Add to this the fact that keyset and dynamic cursors often must hold locks on underlying rows for the entire scope of the cursor, and it is not hard to see why cursors are considered the SQL of last resort. The combination of slow processing and holding locks during the entire course of that processing can result in extreme blocking issues, decreasing overall database performance and scalability.
Lesson 3: Modifying Data
MORE INFO
Locks
If you re not familiar with the SQL Server locking mechanisms, see the Locking in the Database Engine topic in SQL Server 2005 Books Online.
BEST PRACTICES
Try to steer clear of cursors
Avoid cursors whenever possible. Ideally, cursors should be used only for administrative purposes when a set-based solution is impossible to implement.
Quick Check
Which cursor types can detect changes to the underlying data Keyset and dynamic cursors can detect changes to the underlying data.
Quick Check Answer
Creating Local and Global Temporary Tables
When working with complex queries, it is often helpful to break up the logic into smaller, more manageable chunks. Breaking the logic can help simplify queries and stored procedures, especially when iterative logic is necessary. It can also help performance in many cases. If you need to apply the results of a complex query to other queries, it is often cheaper to cache the results of the query in a temporary table and reuse them than to reexecute the complex query each time. You can cache intermediate results in special tables called temporary tables. These tables act just like other SQL Server tables, but they are actually created in the tempdb system database. When you are finished using temporary tables, you do not have to drop them; they are automatically dropped when the connection using them is closed. SQL Server has two types of temporary tables: local and global. Local temporary tables are visible only to the connection that created them. Global temporary tables, on the other hand, are visible to all connections.
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