SQL
Joining Multiple Tables for Comprehensive Data
Combine data from multiple tables using JOIN operations (e.g., LEFT JOIN) to retrieve related information like user details with their order counts.
SELECT u.id, u.username, COUNT(o.order_id) AS total_orders
FROM users u
LEFT JOIN orders o ON u.id = o.user_id
GROUP BY u.id, u.username
HAVING COUNT(o.order_id) > 0;
How it works: This query uses a 'LEFT JOIN' to combine data from the 'users' and 'orders' tables. It retrieves each user's ID, username, and the total number of orders they've placed. The 'LEFT JOIN' ensures all users are included, even those without orders. 'GROUP BY' aggregates the order counts per user, and 'HAVING' filters for users who have placed at least one order.