Objective

Construct an SQL query to identify and list the names of all customers who have never placed an order. Ensure the resulting list is ordered alphabetically by the customers' names.

Additional information

You are provided with two tables:

The customers table:

The orders table:

Your query should return a table with a single column, customer_name, containing the names of customers who have no corresponding entries in the orders table. If every customer has placed at least one order, the query should return an empty result set.

SELECT
    c.customer_name
FROM
    customers c
    LEFT JOIN orders o ON c.customer_id = o.customer_id
WHERE
    o.order_id IS NULL
ORDER BY
    c.customer_name

Explanation

The objective is to list the names of all customers who have never placed an order, sorted alphabetically.

Step 1: LEFT JOIN - include all customers

A LEFT JOIN keeps every row from customers regardless of whether a matching row exists in orders.

FROM customers c
LEFT JOIN orders o ON c.customer_id = o.customer_id

Customers with no orders will have NULL in all orders columns after the join.

Step 2: WHERE - filter to customers with no orders

Keep only rows where the join produced no match (i.e., order_id is NULL).

WHERE o.order_id IS NULL

Step 3: SELECT and ORDER BY - return sorted names

SELECT c.customer_name
...
ORDER BY c.customer_name