题解 | #21年8月份练题总数#
21年8月份练题总数
https://www.nowcoder.com/practice/b8f30b239b454ed490367b53ea95607d
SELECT COUNT(DISTINCT device_id) AS did_cnt,COUNT(question_id) AS question_id FROM question_practice_detail WHERE YEAR(date) = 2021 AND MONTH(date) = 8
COUNT() 聚合函数是计算所有记录条数的总数的,如果参数不具备唯一性,有时候需要用 DISTINCT 关键字做去重复处理。
#练习时长两年半#