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Course

Improving Query Performance in SQL Server

IntermediateSkill Level

4.8+

Updated 02/2023

In this course, students will learn to write queries that are both efficient and easy to read and understand.

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SQLProgramming4 hr16 videos58 Exercises4,450 XP24,822Statement of Accomplishment

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Course Description

A mission critical assignment is depending on your SQL coding skills. You’ve been given some code to fix. It is giving the results you need but it’s running too slow, and it’s poorly formatted making it hard to read. The deadline is tomorrow. You’ll need to reformat the code and try different methods to improve performance. The pressure is on!!! In this course we’ll be using SQL on real world datasets, from sports and geoscience, to look at good coding practices and different ways how we can can improve the performance of queries to achieve the same outcome.

Prerequisites

Intermediate SQL Server

1

Introduction, Review and The Order of Things

In this chapter, students will learn how SQL code formatting, commenting, and aliasing is used to make queries easy to read and understand. Students will also be introduced to query processing order in the database versus the order of the SQL syntax in a query.

Introduction

Formatting - player BMI

Commenting - player BMI

Commenting - how many Kiwis in the NBA?

Ambiguous column names

Aliasing - team BMI

Query order

Processing order

Syntax order - New Zealand earthquakes

Syntax order - Japan earthquakes

Syntax order - very large earthquakes

2

Filtering and Data Interrogation

This chapter introduces filtering with WHERE and HAVING and some best practices for how (and how not) to use these keywords. Next, it explains the methods used to interrogate data and the effects these may have on performance. Finally, the chapter goes over the roles of DISTINCT() and UNION in removing duplicates and their potential effects on performance.

Filtering with WHERE

Column does not exist

Functions in WHERE

Test your knowledge of WHERE

Filtering with HAVING

Row filtering with HAVING

Filtering with WHERE and HAVING

Test your knowledge of HAVING

Interrogation after SELECT

SELECT what you need

Limit the rows with TOP

Should I use ORDER BY?

Managing duplicates

Remove duplicates with DISTINCT()

UNION and UNION ALL

UNION or DISTINCT()?

3

Sub-queries and presence or absence

This chapter is an introduction to sub-queries and their potential impacts on query performance. It also examines the different methods used to determine if the data in one table is present, or absent, in a related table.

Sub-queries

Uncorrelated sub-query

Correlated sub-query

Sub-query vs INNER JOIN

Presence and absence

Interrogating with INTERSECT

Alternative methods 1

IN and EXISTS

NOT IN and NOT EXISTS

NOT IN with IS NOT NULL

Alternative methods 2

Exclusive LEFT OUTER JOIN

Test your knowledge

4

Query performance tuning

Students are introduced to how STATISTICS TIME, STATISTICS IO, indexes, and executions plans can be used in SQL Server to help analyze and tune query performance.

Time statistics

STATISTICS TIME in queries

STATISTICS TIME results

Page read statistics

STATISTICS IO: Example 1

STATISTICS IO: Example 2

STATISTICS IO comparison

Test your knowledge of indexes

Clustered index

Execution plans

Sort operator in execution plans

Test your knowledge of execution plans

Query performance tuning: final notes

Improving Query Performance in SQL Server

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FAQs

What types of performance issues does this course teach me to fix?

You learn to optimize slow queries by improving code formatting, choosing better filtering methods, refining subqueries, and using tools like execution plans, indexes, and STATISTICS IO.

What datasets are used in the exercises?

You work with real-world datasets from sports and geoscience to practice query optimization techniques in SQL Server throughout the four chapters.

Does the course cover execution plans and indexes?

Yes. Chapter 4 introduces STATISTICS TIME, STATISTICS IO, indexes, and execution plans as tools for analyzing and tuning query performance in SQL Server.

Will I learn about the difference between WHERE and HAVING for filtering?

Yes. Chapter 2 covers best practices for using WHERE and HAVING, including common mistakes to avoid and how each filtering approach affects performance.

Is this course specific to SQL Server or applicable to other databases?

The course uses SQL Server and its specific tools like STATISTICS TIME and STATISTICS IO. However, the general principles of query optimization apply broadly to other SQL databases.

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