What is LEFT JOIN?
LEFT JOIN shows ALL rows from the left table, even if no match exists in the right table.
Simple rule: Left table = Always shown, Right table = Only if match
How LEFT JOIN Works
Basic Syntax
SELECT columns
FROM left_table
LEFT JOIN right_table ON left_table.id = right_table.foreign_id;Example: All Students with Orders
SELECT students.name, orders.product
FROM students
LEFT JOIN orders ON students.id = orders.student_id;Result: John, Mary AND Peter (Peter shows NULL for product)
LEFT JOIN vs INNER JOIN
- INNER JOIN → Only matching rows (John, Mary)
- LEFT JOIN → All from left + matches (John, Mary, Peter with NULL)
When to Use
- Find customers who never ordered
- List all products including unsold ones
- Show all employees even without assigned projects
Try It Below
Practice with pre-joined LEFT JOIN results!
What Comes Next
Next: RIGHT JOIN - opposite of LEFT JOIN.