整理了五种解题方法 # 当作日期处理 # 1 SELECT DAY(date) as day,count(device_id) as question_cnt FROM question_practice_detail WHERE DATE_FORMAT(date,'%Y-%m') = '2021-08' group by DAY(date) # #2 SELECT DAY(date) as day,count(device_id) as question_cnt FROM question_practice_detail WHERE YEAR(date) = '2021' ...