9. Using SQL to Uncover the Truth – a Case Study

Learning Objectives

By the end of this chapter, you will be able to:

• Use the scientific method and critical thinking to glean insights about your data
• Solve real-world problems outside of those described within this book by using the skills that you have acquired
• Convert data and hypotheses into actionable tasks and insights
• Use the skills developed in this book to solve problems in your specific problem domain

In this chapter, we will examine an extensive and detailed real-world case study of sales data. This case study will not only demonstrate the processes used in SQL analysis to find solutions for actual problems but will also provide you with confidence and experience in solving such problems.

Introduction

Throughout SQL for Data Analytics, you have learned a range of new skills, including basic descriptive statistics, SQL commands and importing and exporting data in PostgreSQL, as well as more advanced methods, such as functions and triggers. In this final chapter of the book, we will combine these new skills with the scientific method and critical thinking to solve the real-world problem of understanding the cause of an unexpected drop in sales. This chapter provides a case study and will help you to develop confidence in applying your new SQL skillset to your own problem domains. To solve the problem presented in this use case, we will use the complete range of your newly developed skills, from using basic SQL searches to filter out the available information to aggregating and joining multiple sets of information and using windowing methods to group the data in a logical manner. By completing case studies such as this, you will refine one of the key tools in your data...

Case Study

Throughout this chapter, we will cover the following case study. The new ZoomZoom Bat Scooter is now available for sale exclusively through its website. Sales are looking good, but suddenly, pre-orders start plunging by 20% after a couple of weeks. What's going on? As the best data analyst at ZoomZoom, it's been assigned to you to figure it out.

Scientific Method

In this case study, we will be following the scientific method to help solve our problem, which, at its heart, is about testing guesses (or hypotheses) using objectively collected data. We can decompose the scientific method into the following key steps:

1. Define the question to answer what caused the drop-in sales of the Bat Scooter after approximately 2 weeks.
2. Complete background research to gather sufficient information to propose an initial hypothesis for the event or phenomenon.
3. Construct a hypothesis to explain the event or answer the question.
4. Define and execute an...

Summary

Congratulations! You have just completed your first real-world data analysis problem using SQL. In this chapter, you developed the skills necessary to develop hypotheses for problems and systematically gather the data required to support or reject your hypothesis. You started this case study with a reasonably difficult problem of explaining an observed discrepancy in sales data and discovered two possible sources (launch timing and marketing campaign) for the difference while rejecting one alternative explanation (sales price). While being a required skill for any data analyst, being able to understand and apply the scientific method in our exploration of problems will allow you to be more effective and find interesting threads of investigation. In this chapter, you used the SQL skills developed throughout this book; from simple SELECT statements to aggregating complex datatypes as well as windowing methods. After completing this chapter, you will be able to continue and repeat...