LEFT JOIN - Keep All Left Rows

LEFT JOIN keeps ALL rows from the left table, even if there's no match on the right.

SELECT e.first_name, d.name AS department_name
FROM employees e
LEFT JOIN departments d
ON e.department_id = d.id;

If an employee has no matching department, department_name will be NULL.

INNER JOIN vs LEFT JOIN:

• INNER JOIN: only matching rows
• LEFT JOIN: all left rows + matching right rows

LEFT JOIN is essential for finding missing relationships and ensuring no data is lost.