php - adddate(curdate(), -(day(curdate())-1)) および concat(last_day(curdate()),' 23:59:59')

Question

この mysql スクリプトは正確には時間を BETWEEN とは何ですか?

     ADDDATE(CURDATE(), -(DAY(CURDATE())-1)) AND CONCAT(LAST_DAY(CURDATE()),' 23:59:59')