Lesson 13 / 30

LEFT & RIGHT JOIN

Keep unmatched rows with LEFT and RIGHT JOIN, and find records with no match using IS NULL.

LEFT JOIN

LEFT JOIN keeps every row from the left table, filling unmatched right-side columns with NULL.

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

Output:

name        | order_id
Asha Rao    | 1
Rahul Mehta | 2
Priya Nair  | NULL

RIGHT JOIN is the mirror of LEFT JOIN — it keeps every row from the right table instead. Most people just swap table order and use LEFT JOIN.

Add WHERE o.id IS NULL after a LEFT JOIN to find customers with no orders at all.