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MySQL Joins and Aggregation

📅 2026-06-12 | 📂 MySQL

Joins

SELECT users.name, orders.product
FROM users
INNER JOIN orders ON users.id = orders.user_id;

SELECT users.name, orders.product
FROM users
LEFT JOIN orders ON users.id = orders.user_id;

Aggregation

SELECT age, COUNT(*) as count FROM users GROUP BY age;
SELECT SUM(amount) FROM orders WHERE user_id = 1;

Summary

INNER JOIN returns matching rows from both tables
LEFT JOIN returns all rows from left table