Which query includes all orders and their customers, even if an order has no customer (rare scenario)?

• A. SELECT * FROM orders o INNER JOIN customers c ON o.customer_id = c.id;
• B. SELECT * FROM orders o LEFT JOIN customers c ON o.customer_id = c.id;
• C. SELECT * FROM orders o FULL JOIN customers c ON o.customer_id = c.id;
• D. SELECT * FROM orders o RIGHT JOIN customers c ON o.customer_id = c.id;

Answer: (A)

The idea is to keep every order and bring in the related customer data when it exists. That’s exactly what a left outer join does: it returns all rows from the orders table and, where there’s a matching customer, fills in the customer fields; where there isn’t a match, those customer fields are NULL. So the query you want is: SELECT * FROM orders o LEFT JOIN customers c ON o.customer_id = c.id; If an order has no customer, the order still appears with NULLs in the customer columns. An inner join would drop such orders, which isn’t desirable here. A full join would also include customers with no orders, and a right join would preserve all customers instead of all orders, so they don’t fit the requirement.