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?

Aliasing

Ambiguous column names

Aliasing - team BMI

Query order

Processing order

Syntax order - New Zealand earthquakes

Syntax order - Japan earthquakes

Syntax order - very large earthquakes

 Introduction, Review and The Order of Things

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()?

Filtering and Data Interrogation

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

INTERSECT

EXCEPT

Interrogating with INTERSECT

Alternative methods 1

IN and EXISTS

NOT IN and NOT EXISTS

NOT IN with IS NOT NULL

Alternative methods 2

INNER JOIN

Exclusive LEFT OUTER JOIN

Test your knowledge

Sub-queries and presence or absence

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.

STATISTICS TIME

STATISTICS TIME dans les requêtes

Résultats de STATISTICS TIME

Statistiques de lecture de pages

STATISTICS IO : Exemple 1

STATISTICS IO : Exemple 2

Comparaison de STATISTICS IO

Index

Testez vos connaissances sur les index

Index cluster

Plans d’exécution

Opérateur Sort dans les plans d’exécution

Testez vos connaissances sur les plans d’exécution

Optimisation des performances des requêtes : notes finales

Query performance tuning

Orders dataset

NBAPlayers dataset

NBATeams dataset

NBAPlayersStatistics dataset

Une mission critique repose sur vos compétences en SQL. On vous a confié du code à corriger. Il renvoie bien les résultats attendus, mais il est trop lent et mal formaté, ce qui le rend difficile à lire. L’échéance est demain. Vous devrez reformater le code et essayer différentes méthodes pour améliorer les performances. La pression monte ! Dans ce cours, nous utiliserons SQL sur des jeux de données réels, issus du sport et des géosciences, pour étudier les bonnes pratiques de codage et différentes manières d’améliorer les performances des requêtes tout en aboutissant au même résultat.

Intermediate SQL Server

Découvrez comment reformater le code et améliorer les requêtes SQL. Appliquez vos compétences aux données.

Améliorer les performances des requêtes dans SQL Server

Dans ce cours, les étudiants apprendront à rédiger des requêtes à la fois efficaces et faciles à lire et à comprendre.

Développeur SQL Server

SQL Server pour les administrateurs de bases de données

Testez vos connaissances sur les index

Exercice interactif pratique