Data Engineering for Beginners

CHAPTER 4SQL Fundamentals

In the previous chapter, you learned about the foundations of databases, what they are and how they’re structured. Now it’s time to explore SQL, the language used to communicate with relational databases. As a data engineer, you’ll find that SQL will become one of your most-used tools. Whether you’re extracting insights, transforming data, or building pipelines, you’ll need to write queries. In this chapter, we’re going to walk you through SQL fundamentals and look at simple code examples. By the end of this chapter, you’ll be able to analyze data and apply what you’ve learned using a database management system.

HERE’S WHAT WE’LL COVER:

• What SQL is and why it’s important
• Basic SELECT queries
• Filtering using the WHERE statement and logical operators
• Using JOINs to combine data
• Aggregating data with GROUP BY and functions
• Writing subqueries and using window functions
• Setting up SQL Server and running queries
• Best practices for writing clean and efficient SQL

Introduction to SQL

SQL is a programming language used to communicate with and manage data stored in relational databases. Think of it as a tool used to ask questions and give instructions to a database. To maintain clarity and consistency throughout this chapter, we’ll rely on two tables for most of our examples: a Customer table that stores customer information and an Orders table that stores all orders and the total amount for the store.

Customer Table

CUSTOMER_ID	CUSTOMER_NAME	STATUS ...