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Learn T-SQL Querying

You're reading from   Learn T-SQL Querying A guide to developing efficient and elegant T-SQL code

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Product type Paperback
Published in May 2019
Publisher Packt
ISBN-13 9781789348811
Length 484 pages
Edition 1st Edition
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Authors (2):
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Pedro Lopes Pedro Lopes
Author Profile Icon Pedro Lopes
Pedro Lopes
Pam Lahoud Pam Lahoud
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Pam Lahoud
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Table of Contents (18) Chapters Close

Preface 1. Section 1: Query Processing Fundamentals FREE CHAPTER
2. Anatomy of a Query 3. Understanding Query Processing 4. Mechanics of the Query Optimizer 5. Section 2: Dos and Donts of T-SQL
6. Exploring Query Execution Plans 7. Writing Elegant T-SQL Queries 8. Easily-Identified T-SQL Anti-Patterns 9. Discovering T-SQL Anti-Patterns in Depth 10. Section 3: Assemble Your Query Troubleshooting Toolbox
11. Building Diagnostic Queries Using DMVs and DMFs 12. Building XEvent Profiler Traces 13. Comparative Analysis of Query Plans 14. Tracking Performance History with Query Store 15. Troubleshooting Live Queries 16. Managing Optimizer Changes with the Query Tuning Assistant 17. Other Books You May Enjoy

The perils of SELECT *

SELECT * should be avoided in stored procedures, views, and multi-statement table-valued functions (MSTVF) because our T-SQL code might break if there are any changes to the underlying schema. For example, applications that reference SELECT * may be relying on the ordinal position rather than column names and may encounter errors if the underlying table definition is changed. Instead, fully qualify the names of columns that are relevant for our result set.

This also has important performance implications. Some application patterns may rely on reading an entire dataset and applying filters in the client layer only. For example, imagine a web application where a sales supervisor can see a report of orders registered for a given month, with details per product. The application connects to the AdventureWorks sample database and runs a query:

Dim sqlConnection1...
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