The SQL Workshop: Learn to create, manipulate and secure data and manage relational databases with SQL

The SQL Workshop

Copyright © 2019 Packt Publishing

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Authors: Frank Solomon, Prashanth Jayaram, and Awni Al Saqqa

Reviewers: Tor Harrington, Pradeep Kumar Gupta, Aaditya Pokkunuri, Shubham Jain, Fiodar Sazanavets, Shashikant Shakya, and Trevoir Williams

Managing Editor: Manasa Kumar

Acquisitions Editors: Alicia Wooding and Karan Wadekar

Production Editor: Salma Patel

Editorial Board: Shubhopriya Banerjee, Bharat Botle, Ewan Buckingham, Megan Carlisle, Mahesh Dhyani, Manasa Kumar, Alex Mazonowicz, Bridget Neale, Dominic Pereira, Shiny Poojary, Abhishek Rane, Brendan Rodrigues, Mugdha Sawarkar, Erol Staveley, Ankita Thakur, Nitesh Thakur, and Jonathan Wray

First published: December 2019

Production reference: 2291220

ISBN 978-1-83864-235-8

Published by Packt Publishing Ltd.

Livery Place, 35 Livery Street

Birmingham B3 2PB, UK

Table of Contents

Preface

1. SQL Basics

Introduction

Understanding Data

An Overview of Basic SQL Commands

Creating Databases

The Use of Semicolons

Data Types in SQL

Creating Simple Tables

Exercise 1.01: Building the PACKT_ONLINE_SHOP Database

Populating Your Tables

Exercise 1.02: Inserting Values into the Customers Table of the PACKT_ONLINE_SHOP Database

Activity 1.01: Inserting Values into the Products Table in the PACKT_ONLINE_SHOP Database

Summary

2. Manipulating Data

Introduction

The INSERT Operation

Performing a Simple INSERT

Exercise 2.01: Inserting One Row of Data into a Table

Multiple Inserts

Exercise 2.02: Specifying Default Values

Using an INSERT Statement to Add Data from Another Dataset

The DELETE Operation

Exercise 2.03: Deleting a record from a table

The ALTER Operation

Exercise 2.04: Manipulating the Auto-Increment Values in a Table

The UPDATE Operation

The Basic UPDATE Statement

ALIASING

Conditional Update of Records

Limiting the Records Using an UPDATE Statement

Exercise 2.05: UPDATE Using Computed Values

The DROP Operation

Activity 2.01: Inserting Additional values to the Products table

Summary

3. Normalization

Introduction

Primary Key Constraints

Foreign Key Constraints

Preserving Data Integrity

Types of Data Integrity

The Concept of Normalization

First Normal Form (1NF)

Second Normal Form (2NF)

Third Normal Form (3NF)

Denormalization

Exercise 3.01: Building a Relationship between Two Tables

Activity 3.01: Building a Relationship between the Orders and the OrderItems table

Summary

4. The SELECT Statement

Introduction

What Does the SELECT Statement Do?

Retrieving All Columns of a Table

Selecting Limited Columns

Exercise 4.01: Selecting Columns from a Table

Using Naming Aliases

Exercise 4.02: Aliasing the Column Headers

Activity 4.01: Displaying Particular Columns from the Table

Ordering Results

Ordering Rows According to a Particular Column

Ordering Rows According to Multiple Columns

Using LIMIT

Exercise 4.03: Using the LIMIT Keyword

Using DISTINCT

Using Mathematical Expressions

Exercise 4.04: Calculating the Line Item Total

Exercise 4.05: Calculating Discount

Activity 4.02: Extracting the Top Five Highest Priced Items

Summary

5. Shaping Data with the WHERE Clause

Introduction

The WHERE Clause Syntax

Exercise 5.01: Implementing Logical Operators in the WHERE Clause

Exercise 5.02: Using the BETWEEN Operator

The Not Equal Operator

Exercise 5.03: Using the != and <> Operators

The LIKE Operator

Exercise 5.04: Using the LIKE Operator to Check a Pattern at the Beginning of a String

Exercise 5.05: Using the LIKE Operator to Check for a Specified Length

Checking for NULLS

Exercise 5.06: Searching for NULL Values

Combining Conditions with the AND, OR, and NOT Operators

Exercise 5.07: Querying Multiple Conditions

Activity 5.01: Combining Conditions to Extract Store Data

Summary

6. JOINS

Introduction

INNER JOIN

Exercise 6.01: Extracting Orders and Purchaser Information

RIGHT JOIN

Exercise 6.02: Implementing RIGHT JOIN

LEFT JOIN

Exercise 6.03: Implementing LEFT JOIN

CROSS JOIN

Exercise 6.04: Implementing CROSS JOINS

UNION JOIN

Exercise 6.05: Implementing a UNION JOIN

Activity 6.01: Implementing JOINS

Summary

7. Subqueries, Cases, and Views

Introduction

Subqueries

Exercise 7.01: Working with Subqueries

Activity 7.01: Finding the Product Category Name Using a Subquery

Case Statements

Exercise 7.02: Using Case Statements

Activity 7.02: Categorizing the Shipments Using CASE Statements

Views

Exercise 7.03: Building a View

Activity 7.03: Building a View

Summary

8. SQL Programming

Introduction

Programming for SQL Products – The Basics

Stored Procedures

Exercise 8.01: Building a MySQL Stored Procedure That Returns a List of Packt Online Shop Order Details

Exercise 8.02: Altering a MySQL Stored Procedure

Activity 8.01: Building a Stored Procedure

Functions

Exercise 8.03: Build a MySQL Function

Activity 8.02: Working with MySQL Functions

Triggers

Exercise 8.04: Build a MySQL Trigger

Activity 8.03: Building a Trigger

Summary

9. Security

Introduction

Access Control (Authorization)

Exercise 9.01: Creating New MySQL users

Exercise 9.02: Granting EXECUTE permission in MySQL

Activity 9.01: Grant UPDATE permission on a table in MySQL

Summary

10. Aggregate Functions

Introduction

Aggregate Functions (SUM, COUNT, AVG, MIN, and MAX) and the GROUP BY Clause

Exercise 10.01: Implementing Aggregate Functions

The HAVING Clause

Exercise 10.02: Implementing the HAVING Clause

The Differences between the SQL HAVING and WHERE Clauses

SQL OVER and PARTITION BY

The RANK and DENSE_RANK Functions

Exercise 10.03: Implementing RANK

Activity 10.01: Working with Aggregates

Summary

11. Advanced SQL

Introduction

String Functions

Exercise 11.01: Building a MySQL Query that Returns the OrderID, Quantity, and Notes Columns

Exercise 11.02: Using LIKE in a Stored Procedure

Activity 11.01: Implementing the LIKE Operator

Dealing with NULL and COALESCE

The COALESCE Function

Exercise 11.03: Using the COALESCE Function to Handle a NULL Value in a Combined Set of Values

Finding Duplicate Table Rows

Transactions

Activity 11.02: Using Transactions

Summary

Appendix

Preface

About

This section briefly introduces the coverage of this book, the technical skills you'll need to get started, and the software requirements required to complete all of the included activities and exercises.

About the Book

Many software applications are backed by powerful relational database systems, meaning that the skills to be able to maintain a SQL database and reliably retrieve data are in high demand. With its simple syntax and effective data manipulation capabilities, SQL enables you to manage relational databases with ease. The SQL Workshop will help you progress from basic to advanced-level SQL queries in order to create and manage databases successfully.

This Workshop begins with an introduction to basic CRUD commands and gives you an overview of the different data types in SQL. You’ll use commands for narrowing down the search results within a database and learn about data retrieval from single and multiple tables in a single query. As you advance, you’ll use aggregate functions to perform calculations on a set of values, and implement process automation using stored procedures, functions, and triggers. Finally, you’ll secure your database against potential threats and use access control to keep your data safe.

Throughout this Workshop, you’ll use your skills on a realistic database for an online shop, preparing you for solving data problems in the real world.

By the end of this book, you’ll have built the knowledge, skills and confidence to creatively solve real-world data problems with SQL.

About the Chapters

Chapter 1, SQL Basics, explains how to create a simple database and how to create tables within databases. We will also learn how to populate data within a table.

Chapter 2, Manipulating Data, guides us through how to alter tables and delete and update entries within a table.

Chapter 3, Normalization, explains how to normalize tables within a database such that data integrity is maintained.

Chapter 4, The SELECT Statement, covers how to write basic queries to retrieve data from the database.

Chapter 5, Shaping Data with the WHERE Clause, covers implementing conditional clauses within our queries such that we get fine-grained control over our data.

Chapter 6, JOINS, talks about retrieving data from multiple tables by performing various join operations.

Chapter 7, Subqueries, Cases, and Views, talks about ways to retrieve data from intermediary tables using views and then sub-queries to further filter down results.

Chapter 8, SQL Programming, talks about advanced SQL concepts such as the functions and triggers.

Chapter 9, Security, looks at providing and revoking access to users on tables and databases.

Chapter 10, Aggregate Functions, teaches how use SQL aggregate functions and how to solve problems with them. We will also look at advanced clauses, such as the GROUP BY and the HAVING clauses, and see how they can help us to fine-tune our results

Chapter 11, Advanced SQL, looks at functions in SQL and how they can be used as powerful filtering tools.

Conventions

Code words in text, database table names, screen text, folder names, filenames, file extensions, pathnames, dummy URLs, user input, and Twitter handles are shown as follows: We'll start with the Orders table since the Orders table ties the orders together with the OrderItems table.

A block of code is set as follows:

USE PACKT_ONLINE_SHOP;

Before You Begin

Each great journey begins with a humble step. Our upcoming adventure in the land of SQL is no exception. Before you can begin, you need to be prepared with the most productive environment. In this section, you will see how to do that.

To Install MySQL

To install MySQL, follow the steps present in the following documentation: https://packt.live/2rxXXv1

To Install the Code Bundle

Download the code files from GitHub at https://packt.live/2QCKNqB and place them in a new folder called C:\Code on your local system. Refer to these code files for the complete code bundle.

1. SQL Basics

Overview

This chapter covers the very basic concepts of SQL that will get you started with writing simple commands. By the end of this chapter, you will be able to identify the difference between structured and unstructured data, explain the basic SQL concepts, create tables using the CREATE statement, and insert values into tables using SQL commands.

Introduction

The vast majority of companies today work with large amounts of data. This could be product information, customer data, client details, employee data, and so on. Most people who are new to working with data will do so using spreadsheets. Software such as Microsoft Excel has many tools for manipulating and analyzing data, but as the volume and complexity of the data you're working with increases, these tools may become inefficient.

A more powerful and controlled way of working with data is to store it in a database and use SQL to access and manipulate it. SQL works extremely well for organized data and can be used very effectively to insert, retrieve, and manipulate data with just a few lines of code. In this chapter, we'll get an introduction to SQL and see how to create databases and tables, as well as how to insert values into them.

Understanding Data

For most companies, storing and retrieving data is a day-to-day activity. Based on how data is stored, we can broadly classify data as structured or unstructured. Unstructured data, simply put, is data that is not well-organized. Documents, PDFs, and videos fall into this category—they contain a mixture of different data types (text, images, audio, video, and so on) that have no consistent relationship between them. Media and publishing are examples of industries that deal with unstructured data such as this.

In this book, our focus will be on structured data. Structured data is organized according to a consistent structure. As such, structured data can be easily organized into tables. Thanks to its consistent organization, working with structured data is easier, and it can be processed more effectively. Tables are collections of entities or tuples (rows) and attributes (columns).

For example, consider the following table:

Figure 1.1: An example student's database table

For each row, there is a clear relationship; a given student takes a particular subject and achieves a specific score in that subject. The columns are also known as fields, while the rows are known as records.

Data that is presented in tabular form can be stored in a relational database. Relational databases, as the name suggests, store data that has a certain relationship with another piece of data. A Relational Database Management System (RDBMS) is a system that's used to manage relational data. SQL works very well with relational data. Popular RDBMSs include Microsoft SQL Server, MySQL, and Oracle. Throughout this book, we will be working with MySQL. We can use various SQL commands to work with data in relational databases. We'll have a brief look at them in the next section.

An Overview of Basic SQL Commands

SQL (often pronounced sequel) stands for Structured Query Language. A query in SQL is constructed using different commands. These commands are classified into what are called sublanguages of SQL. Even if you think you know them already, give this a read to see if these seem more relatable to you. There are five sublanguages in SQL, as follows:

Data Definition Language (DDL): As the name suggests, the commands that fall under this category work with defining either a table, a database, or anything within. Any command that talks about creating something in SQL is part of DDL. Some examples of such commands are