SQL
Retrieving Related Data with LEFT JOIN
Master the LEFT JOIN to combine rows from two tables, ensuring all records from the left table are included, even if no match exists in the right table for related data.
SELECT u.user_id, u.username, p.post_title, p.created_at
FROM users u
LEFT JOIN posts p ON u.user_id = p.author_id
WHERE u.status = 'active'
ORDER BY u.username, p.created_at DESC;
How it works: This query uses a `LEFT JOIN` to retrieve all active users and their associated posts. If a user has no posts, their `user_id` and `username` will still appear, but `post_title` and `created_at` will be `NULL`. This is ideal for scenarios like displaying user profiles that might or might not have related content, ensuring all main entities are always shown.