Answer
An inner join returns only matching combinations, while an outer join also preserves selected unmatched rows. • LEFT preserves unmatched left rows. • RIGHT preserves unmatched right rows, and FULL preserves both sides. • Outer-join filters must be placed carefully to avoid removing preserved rows.
💡 SQL Example
SELECT c.name, o.order_id FROM customers c LEFT JOIN orders o ON o.customer_id = c.customer_id;
Result
Customers with and without orders
⚡ Quick Revision
Inner joins keep matches; outer joins can also keep unmatched rows.