Book Image

Learn T-SQL Querying

By : Pedro Lopes, Pam Lahoud
Book Image

Learn T-SQL Querying

By: Pedro Lopes, Pam Lahoud

Overview of this book

Transact-SQL (T-SQL) is Microsoft's proprietary extension to the SQL language used with Microsoft SQL Server and Azure SQL Database. This book will be a usefu to learning the art of writing efficient T-SQL code in modern SQL Server versions as well as the Azure SQL Database. The book will get you started with query processing fundamentals to help you write powerful, performant T-SQL queries. You will then focus on query execution plans and leverage them for troubleshooting. In later chapters, you will explain how to identify various T-SQL patterns and anti-patterns. This will help you analyze execution plans to gain insights into current performance, and determine whether or not a query is scalable. You will also build diagnostic queries using dynamic management views (DMVs) and dynamic management functions (DMFs) to address various challenges in T-SQL execution. Next, you will work with the built-in tools of SQL Server to shorten the time taken to address query performance and scalability issues. In the concluding chapters, this will guide you through implementing various features, such as Extended Events, Query Store, and Query Tuning Assistant, using hands-on examples. By the end of the book, you will have developed the skills to determine query performance bottlenecks, avoid pitfalls, and discover the anti-patterns in use.
Table of Contents (18 chapters)
Free Chapter
1
Section 1: Query Processing Fundamentals
5
Section 2: Dos and Donts of T-SQL
10
Section 3: Assemble Your Query Troubleshooting Toolbox

Understanding predicate SARGability

A predicate is a filter that can be used to determine the set of conditions to apply to a query in order to trim the result set. As we have discussed in previous chapters, these are typically applicable to the following clauses:

  • JOIN clauses, which filter rows matching the type of join
  • HAVING clauses, which filter the results
  • WHERE clauses, which filter source rows from a table or an index

Most queries will make use of predicates, usually through a WHERE clause. When a predicate is serviceable by an index, it is said the predicate is SARGable, which is an acronym for Search ARGument-able. Having SARGable predicates should be a goal for our T-SQL queries, because it can reduce the number of rows which need to be processed by a plan earlier in the execution, when the data is being read by the database engine. The implementation of this early...