CREATE TABLE cart_items (
    id CHAR(36) PRIMARY KEY,
    cart_id CHAR(36) NOT NULL,
    product_id CHAR(36) NOT NULL,
    quantity INT NOT NULL CHECK (quantity > 0),
    added_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
    FOREIGN KEY (cart_id) REFERENCES carts(id) ON DELETE CASCADE,
    FOREIGN KEY (product_id) REFERENCES products(id) ON DELETE CASCADE,
    INDEX idx_cart_id (cart_id),
    INDEX idx_product_id (product_id),
    UNIQUE KEY unique_cart_product (cart_id, product_id)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_unicode_ci;