SQL — Left Join

Basic LEFT JOIN

SELECT u.name, o.total
FROM users u
LEFT JOIN orders o ON u.id = o.user_id;

All users with orders

-- Users without orders will have NULL
SELECT u.name, o.total
FROM users u
LEFT JOIN orders o ON u.id = o.user_id;

Find users without orders

SELECT u.name
FROM users u
LEFT JOIN orders o ON u.id = o.user_id
WHERE o.id IS NULL;

LEFT JOIN with aggregate

SELECT u.name, COUNT(o.id) AS order_count
FROM users u
LEFT JOIN orders o ON u.id = o.user_id
GROUP BY u.name;

Multiple LEFT JOINs

SELECT u.name, o.total, p.name AS product
FROM users u
LEFT JOIN orders o ON u.id = o.user_id
LEFT JOIN products p ON o.product_id = p.id;

Mini Practice

1. Perform LEFT JOIN
2. Find records without matches
3. Use with aggregate functions
4. Chain multiple LEFT JOINs

Up Next

Continue with Right Join - Right join operations.