How do you include all customers and their orders, even if a customer has none?

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

Answer: (A)

This is about keeping every record from the main table while bringing in related data when it exists. A left join does exactly that: it returns all customers and, for each one, the matching orders. If a customer has no orders, the order fields come back as NULL, but the customer still appears in the result. So the query selects all columns from both tables and joins on the customer_id, preserving every customer even if there are no orders.

If you used a right join, the result would prioritize all orders, not all customers, so customers without orders could be omitted. An inner join would require a matching order for every customer, so those with none would be excluded. A cross join would create a Cartesian product, pairing every customer with every order, which isn’t the intended relationship.