--問1
select items.item_id as 商品ID, items.name as 商品名, items.price as 価格, 
    item_category.name as カテゴリ名 from items inner join item_category using(category_id);
    
--問2
select orders.order_id as 注文ID, orders.order_time as 注文日時, users.name as ユーザー名, 
    items.name as 商品名, items.price as 価格, order_items.quantity as 数量 from order_items
    inner join orders using(order_id)
    inner join items using(item_id)
    inner join users using(user_id) order by orders.order_time;