1.日毎 group by date(created) 2.周毎 ・日曜日開始 group by date(created + interval 1 - DAYOFWEEK(created) day) ・月曜日開始 group by date(created - interval (5 + DAYOFWEEK(created))%7 day) 3.月毎 group by date(created + interval 1 - DAYOFMONTH(created) day) 或いは group by date_format(created, '%Y-%m') ※createdのデータ型はDATETIME