MySQL基础练习题34-游戏玩法分析4

题目

报告在首次登录的第二天再次登录的玩家的比率，四舍五入到小数点后两位。换句话说，你需要计算从首次登录日期开始至少连续两天登录的玩家的数量，然后除以玩家总数。

准备数据

sql 复制代码

## 创建库
create database db;
use db;

## 创建表
Create table If Not Exists Activity (player_id int, device_id int, event_date date, games_played int)

## 向表中插入数据
Truncate table Activity
insert into Activity (player_id, device_id, event_date, games_played) values ('1', '2', '2016-03-01', '5')
insert into Activity (player_id, device_id, event_date, games_played) values ('1', '2', '2016-03-02', '6')
insert into Activity (player_id, device_id, event_date, games_played) values ('2', '3', '2017-06-25', '1')
insert into Activity (player_id, device_id, event_date, games_played) values ('3', '1', '2016-03-02', '0')
insert into Activity (player_id, device_id, event_date, games_played) values ('3', '4', '2018-07-03', '5')

activity表

分析数据

只有 ID 为 1 的玩家在第一天登录后才重新登录，所以答案是 1/3 = 0.33

第一步：选出每个用户id的首次登陆日期

sql 复制代码

select player_id, min(event_date) as login
from activity
group by player_id

第二步：添加连续两次登录的条件

sql 复制代码

select a.event_date fraction
from
    (select player_id, min(event_date) as login
     from activity
     group by player_id) p
        left join activity a
                  on p.player_id=a.player_id and datediff(a.event_date, p.login)=1;

第三步：算出首次登录的第二天再次登录的玩家的 比率，并四舍五入

sql 复制代码

select round(avg(a.event_date is not null), 2) fraction
from
    (select player_id, min(event_date) as login
     from activity
     group by player_id) p
        left join activity a
 on p.player_id=a.player_id and datediff(a.event_date, p.login)=1;

总结

计算首次日期或最小日期可以使用min()函数

使用DATEDIFF()函数来计算两个日期之间的差值