DataBolt

All Lessons

Introduction to SQL

SQL Lesson 1: Your Sample Database

SQL Lesson 2: SELECT — Reading data

SQL Lesson 3: WHERE — Filtering rows

SQL Lesson 4: AND, OR, NOT

SQL Lesson 5: BETWEEN, IN, LIKE

SQL Lesson 6: NULL — The Mystery Value

SQL Lesson 7: ORDER BY

SQL Lesson 8: LIMIT & OFFSET

SQL Lesson 9: Aggregate Functions

SQL Lesson 10: GROUP BY

SQL Lesson 11: HAVING

SQL Lesson 12: INNER JOINs

SQL Lesson 13: LEFT JOINs

SQL Lesson 14: RIGHT JOINs

SQL Lesson 15: SELF JOINs

SQL Lesson 16: UNION JOINs

SQL Lesson 17: Joining Multiple Tables

SQL Lesson 18: Subqueries

SQL Lesson 19: CTEs (WITH)

SQL Lesson 20: CASE Statements

SQL Lesson 21: Window Functions

SQL Lesson 22: String Functions

SQL Lesson 23: Date & Time Functions

SQL Lesson 24: INSERT, UPDATE, DELETE

SQL Lesson 25: CREATE TABLE & DDL

SQL Lesson 26: Indexes & Performance

SQL Lesson 27: Transactions & ACID

SQL Lesson 28: SQL Execution Order

SQL Lesson 29: 50 Practice Problems

CHAPTER 18

JOINing Three+ Tables

Aggregating by category — the analytics workhorse.

IN THIS CHAPTER

Joining three tables in one query
Aliasing tables to keep queries readable
Understanding JOIN order and performance

Customer names, order dates, and product names in each order

SELECT c.name AS customer, o.order_date, p.name AS product, oi.qty,
oi.unit_price
FROM orders o
JOIN customers c ON o.customer_id = c.customer_id
JOIN order_items oi ON o.order_id = oi.order_id
JOIN products p ON oi.product_id = p.product_id
ORDER BY o.order_date, c.name;

✅ Pro Tips: Always use short, meaningful table aliases (c for customers, o for orders, p for products). Avoid single letters where they are ambiguous. In a 6-table JOIN, good aliases are the difference between readable code and maintenance hell.

Included Tables in Exercise

Table: Orders

order_id	customer_id	order_date	total	status
1	1	2024-01-15	79999	completed
2	2	2024-01-20	3498	completed
3	1	2024-02-10	65000	completed
4	3	2024-02-14	499	pending
5	2	2024-03-01	248	completed
6	5	2024-03-15	2999	shipped
7	1	2024-04-05	149	completed

Table: Customers

customer_id	name	city	country
1	Ananya	Hyderabad	India
2	Rohan	Bangalore	India
3	Sam	Mumbai	India
4	Lisa	London	UK
5	Ravi	Delhi	India

Table: order_items

item_id	order_id	product_id	qty	unit_price
1	1	1	1	79999
2	2	3	1	2999
3	2	2	1	499
4	3	5	1	65000
5	4	2	1	499
6	5	4	2	99
7	5	6	1	50
8	6	3	1	2999

Table: products

product_id	name	category	price	stock
1	iPhone 15	Electronics	79999	50
2	SQL Book	Books	499	200
3	Headphones	Electronics	2999	75
4	Notebook	Stationery	99	500
5	Laptop	Electronics	65000	20
6	Pen Set	Stationery	149	0
7	Mouse	Electronics	599	25

Exercise 👇

Exercise:

Tasks

1.👉Show customer names along with their order totals.

2.Show customer names and their order dates.

3.Find customers who have completed orders.

4.Show product names along with quantity ordered.

5.Find total amount spent by each customer.

6.Find number of orders placed by each customer (include customers with no orders).

7.Find total quantity sold for each product.

8.Show customer name, product name, and quantity ordered (combine all tables).

Stuck? Read this task's