Let’s say we want to find all orders placed by a particular customer. We can do this by joining the customers and orders tables together using the relationship established by the customer_id key.

all-orders-placed-by-a-customer

select order_date, order_amount
from customers
join orders
   on customers.customer_id = orders.customer_id
where customer_id = 3

I created the customers and orders tables in MySQL 5.7 in order to follow along with your tutorial. When I tried the above command I got two errors:

ERROR 1054 (42S22): Unknown column 'order_amount' in 'field list'
ERROR 1052 (23000): Column 'customer_id' in where clause is ambiguous

The first was easily fixed by changing order_amount to amount, since that was the name of the column in the orders table.

The second I had to dig around for, and to reproduce the results shown on the webpage I found this query to be satisfactory:

SELECT order_id, order_date, amount
FROM orders
JOIN customers
ON customers.customer_id = orders.customer_id
WHERE orders.customer_id = 3;

Is the query posted on the webpage a typo, or is there just some difference between how the JOIN command is run on different SQL implementations?

To echo the above comment, I believe there is a typo in this query. In order to have order_id included in the results as shown, the query should be:

SELECT order_id, order_date, order_amount
FROM customers
JOIN orders
ON customers.customer_id = orders.customer_id
WHERE customer_id = 3