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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

Understanding QTA fundamentals

While guiding us through the recommended process, QTA doesn't follow it exactly. The very last step 5 will not have the same outcome as we saw in the previous section: instead of providing options to revert to a last known good plan, QTA helps to find a new state that is not the pre-CE upgrade or post-CE upgrade plan, but a new plan that will hopefully outperform both of the previous plans.

The following diagram summarizes the recommended steps to minimize risk with CE upgrades using QTA, which replaces the very last step of the process described in the Understanding where QTA is needed section:

How does QTA find a better query plan for regressed queries? Starting with the same data that's available in Query Store's Regressed Queries report, QTA will look for query patterns that may be affected by changes in CE, specifically from...

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