Sql Joins Cheatsheet

Content

-- SQL joins cheat sheet

-- INNER JOIN: rows matching in both tables
SELECT u.name, o.total
FROM users u
INNER JOIN orders o ON o.user_id = u.id;

-- LEFT JOIN: all users, orders when present
SELECT u.name, o.total
FROM users u
LEFT JOIN orders o ON o.user_id = u.id;

-- RIGHT JOIN: all orders, users when present
SELECT u.name, o.total
FROM users u
RIGHT JOIN orders o ON o.user_id = u.id;

-- FULL OUTER JOIN (when supported)
SELECT u.name, o.total
FROM users u
FULL OUTER JOIN orders o ON o.user_id = u.id;

-- Anti-join: users with no orders
SELECT u.*
FROM users u
LEFT JOIN orders o ON o.user_id = u.id
WHERE o.id IS NULL;

-- Self join
SELECT e.name AS employee, m.name AS manager
FROM employees e
LEFT JOIN employees m ON m.id = e.manager_id;

-- Tip: filter on the outer table in WHERE carefully —
-- predicates on the right table of a LEFT JOIN can turn it into an INNER JOIN.