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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 Feb 2024
Publisher Packt
ISBN-13 9781837638994
Length 456 pages
Edition 2nd Edition
Languages
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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. Part 1: Query Processing Fundamentals
2. Chapter 1: Understanding Query Processing FREE CHAPTER 3. Chapter 2: Mechanics of the Query Optimizer 4. Part 2: Dos and Don’ts of T-SQL
5. Chapter 3: Exploring Query Execution Plans 6. Chapter 4: Indexing for T-SQL Performance 7. Chapter 5: Writing Elegant T-SQL Queries 8. Chapter 6: Discovering T-SQL Anti- Patterns in Depth 9. Part 3: Assembling Our Query Troubleshooting Toolbox
10. Chapter 7: Building Diagnostic Queries Using DMVs and DMFs 11. Chapter 8: Building XEvent Profiler Traces 12. Chapter 9: Comparative Analysis of Query Plans 13. Chapter 10: Tracking Performance History with Query Store 14. Chapter 11: Troubleshooting Live Queries 15. Chapter 12: Managing Optimizer Changes 16. Index 17. Other Books You May Enjoy

Optimizing OR logic

A common query pattern involves the need to express several conditions of which at least one must be true to filter the result set, usually with OR logic. Expressing these OR conditions can have serious performance drawbacks and can often be replaced with other constructs that provide better scalability and performance.

The following example shows a query executed in the AdventureWorks sample database that uses an OR condition in the search predicate. The query lists all rows for a specific product, or where the price is set at a predetermined value:

SELECT ProductID, [UnitPrice], [UnitPriceDiscount],
      [UnitPrice] * (1 - [UnitPriceDiscount]) AS FinalUnitPrice,
      [UnitPriceDiscount] + 0.10 AS NewUnitPriceDiscount,
      [UnitPrice] * (1 - 0.30) AS NewFinalUnitPrice
FROM Sales.SalesOrderDetail
WHERE ProductID = 770
     OR UnitPrice = 3399...
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