Provide a specific example when LEFT JOIN needs to be used.

LEFT JOIN is used when you want to get all records from the left table and the matching records from the right table, and if there are no matches, the right side will contain NULLs.

For example, there is a customers table and an orders table. If you want to display all customers and their orders, including those customers who haven't made any orders yet, you use LEFT JOIN:

SELECT customers.id, customers.name, orders.order_id
FROM customers
LEFT JOIN orders ON customers.id = orders.customer_id;

This will give us a complete list of customers, and for those without orders, the fields from the orders table will be NULL.