Querying Data›Core· 40 min read

JOINs — Combining Tables

Pull related data from multiple tables together — like orders with their customer’s name.

What you will learn

Understand why data is split across tables
Join tables with INNER JOIN
Use foreign keys

Related tables

Instead of repeating data, we split it across tables and link them. An orders table stores a user_id that points to the users table — a foreign key.

Picture these two small tables. Notice the orders table does not repeat the customer’s name — it just stores a user_id that matches an id in users:

users.id	users.name
1	Asha
2	Ravi

orders.id	orders.user_id	orders.total
101	1	500
102	2	250
103	1	900

To show each order with its customer’s name, we need data from both tables at once. A JOIN stitches them together by matching the user_id in orders to the id in users.

Note: We make the orders table for real in the Keys & Relationships lesson coming up, so do not worry if you cannot run the join just yet — focus on understanding the idea here. Once both tables exist with the sample rows above, this exact query will work.

INNER JOIN

A JOIN query has three parts. Read them in order, then look at the code:

Choose the columns you want, naming the table for each so MySQL knows where to look: orders.id, users.name, orders.total.
Start from one table: FROM orders.
Attach the other table and say how they match: INNER JOIN users ON orders.user_id = users.id.

Join orders with their user’s name

SELECT orders.id, users.name, orders.total
FROM orders
INNER JOIN users ON orders.user_id = users.id;

For every order, MySQL looks at its user_id, finds the row in users with the matching id, and glues the two rows side by side — so you can pull users.name right next to the order’s details. The table.column naming (like orders.total) avoids confusion when both tables have a column with the same name (both have id).

Note: Output: orders.id users.name orders.total 101 Asha 500 102 Ravi 250 103 Asha 900 Each order now shows the customer’s name instead of a bare user_id. Orders 101 and 103 both belong to user 1, so both show “Asha”. The join looked up the name from the users table for us.

Note: The ON clause says how the tables connect (orders.user_id = users.id). An INNER JOIN returns rows that match in both tables. There are also LEFT/RIGHT joins for including unmatched rows.

Tip: This is the superpower of relational databases — no duplicated data, everything linked. Laravel’s Eloquent makes joins feel effortless with “relationships”, which you will meet next.

Q. What does the ON clause in a JOIN specify?

Answer: ON defines the matching condition between the tables (e.g. orders.user_id = users.id).

✍️ Practice

Create users and orders tables linked by user_id.
Join them to list each order with the customer’s name.

🏠 Homework

Model books and authors in two tables and join them.