力扣高频SQL50题(基础版)——第八天

1 游戏玩法分析 IV

1.1 题目内容

1.1.1 基本题目信息

1.1.2 示例输入输出

1.2 示例sql语句

SELECT ROUND(count(a2.f_date)/(SELECT count(distinct player_id) FROM Activity),2) fraction
FROM Activity a1
INNER JOIN
(
    SELECT player_id,MIN(event_date) f_date
    FROM Activity
    GROUP BY player_id
)a2
ON a1.player_id=a2.player_id AND a1.event_date-a2.f_date=1

1.3 运行截图

2 每位教师所教授的科目种类的数量

2.1 题目内容

2.1.1 基本题目信息

2.1.2 示例输入输出

2.2 示例sql语句

SELECT teacher_id,count(distinct subject_id)  cnt
FROM Teacher
GROUP BY teacher_id

2.3 运行截图

3 查询近30天活跃用户数

3.1 题目内容

3.1.1 基本题目信息

3.1.2 示例输入输出

3.2 示例sql语句

SELECT activity_date day,count(distinct user_Id) active_users
FROM Activity
WHERE activity_date BETWEEN DATE_SUB('2019-07-27',INTERVAL 29 day)  AND  '2019-07-27'
GROUP BY activity_date

3.3 运行截图