Lesson 1 of 10

Joining two tables

13 min
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Goal

Matching rows with INNER JOIN

Explanation

A well-designed database doesn't repeat the customer's name on every order. It stores the name once in the customers table, and each order carries only the customer's ID in its customer_id column.

JOIN then brings the two tables together at query time, like this: FROM orders JOIN customers ON customers.id = orders.customer_id.

A plain JOIN is an INNER JOIN, which keeps only the rows that have a match in both tables. That means a customer with no orders doesn't show up in the result at all, and we'll fix that in the next lesson.

Your task

Show the name and total of every order, sorted from the largest amount to the smallest.

Checks

5 checks

Five rows, one per order
Columns are name and total
Sorted by order amount, largest first
The largest order is Khalid's, at 300
Fahd is left out because he has no orders

Tables in this lesson

CREATE TABLE customers (
  id   INTEGER PRIMARY KEY,
  name TEXT NOT NULL,
  city TEXT NOT NULL
);

CREATE TABLE orders (
  id          INTEGER PRIMARY KEY,
  customer_id INTEGER REFERENCES customers(id),
  total       INTEGER NOT NULL,
  placed_on   TEXT    NOT NULL
);

INSERT INTO customers (id, name, city) VALUES
  (1, 'Layan',  'Riyadh'),
  (2, 'Khalid', 'Jeddah'),
  (3, 'Reem',   'Dammam'),
  (4, 'Fahd',   'Riyadh');

INSERT INTO orders (customer_id, total, placed_on) VALUES
  (1, 120, '2026-09-01'),
  (1,  80, '2026-09-12'),
  (2, 300, '2026-09-03'),
  (3,  45, '2026-09-20'),
  (2,  60, '2026-09-25');

Joining two tables

Explanation

Your task

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