-- =========================================================================
-- BÀI 11: TÌM LOẠI HÀNG MANG LẠI DOANH THU CAO NHẤT
-- Kỹ thuật sử dụng: INNER JOIN, SUM(oi.quantity * oi.price), GROUP BY, ORDER BY DESC, LIMIT 1
-- =========================================================================

USE `labdb`;

-- Cấu trúc bảng liên quan (Schema):
CREATE TABLE IF NOT EXISTS `categories` (
    `id` INT AUTO_INCREMENT PRIMARY KEY,
    `name` VARCHAR(100) NOT NULL,
    `description` VARCHAR(255) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;

CREATE TABLE IF NOT EXISTS `products` (
    `id` INT AUTO_INCREMENT PRIMARY KEY,
    `category_id` INT NOT NULL,
    `name` VARCHAR(150) NOT NULL,
    `price` DECIMAL(15, 2) NOT NULL DEFAULT 0.00
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;

CREATE TABLE IF NOT EXISTS `order_items` (
    `id` INT AUTO_INCREMENT PRIMARY KEY,
    `order_id` INT NOT NULL,
    `product_id` INT NOT NULL,
    `quantity` INT NOT NULL DEFAULT 1,
    `price` DECIMAL(15, 2) NOT NULL
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;

-- Câu truy vấn chính của Bài 11:
SELECT 
    c.id AS category_id,
    c.name AS category_name,
    c.description,
    SUM(oi.quantity) AS total_quantity_sold,
    SUM(oi.quantity * oi.price) AS total_revenue
FROM categories c
INNER JOIN products p ON c.id = p.category_id
INNER JOIN order_items oi ON p.id = oi.product_id
GROUP BY c.id, c.name, c.description
ORDER BY total_revenue DESC
LIMIT 1;