■会員のランクを取得 SELECT users.name,ranks.name FROM users INNER JOIN ranks ON users.rank_id=ranks.id
■会員ランクが有効なユーザーを取得 SELECT users.name FROM user_ranks INNER JOIN users ON user_ranks.user_id=users.id WHERE acquired_date <= '2023-05-22' AND expiration_date >= '2023-05-22'
■特定の会員(user_id:1)への特典を取得 SELECT ranks.discount_percentage FROM ranks INNER JOIN users ON ranks.id=users.rank_id WHERE rand_id='1'
■そのランク(rank_id:1)になる条件を取得 SELECT annual_fee,min_purchases FROM ranks WHERE rand_id='1'