题目
Table: Activity
+--------------+---------+
| Column Name | Type |
+--------------+---------+
| player_id | int |
| device_id | int |
| event_date | date |
| games_played | int |
+--------------+---------+
(player_id, event_date) 是这个表的两个主键
这个表显示的是某些游戏玩家的游戏活动情况
每一行是在某天使用某个设备登出之前登录并玩多个游戏（可能为0）的玩家的记录
请编写一个 SQL 查询，描述每一个玩家首次登陆的设备名称
查询结果格式在以下示例中：
Activity table:
+-----------+-----------+------------+--------------+
| player_id | device_id | event_date | games_played |
+-----------+-----------+------------+--------------+
| 1 | 2 | 2016-03-01 | 5 |
| 1 | 2 | 2016-05-02 | 6 |
| 2 | 3 | 2017-06-25 | 1 |
| 3 | 1 | 2016-03-02 | 0 |
| 3 | 4 | 2018-07-03 | 5 |
+-----------+-----------+------------+--------------+
Result table:
+-----------+-----------+
| player_id | device_id |
+-----------+-----------+
| 1 | 2 |
| 2 | 3 |
| 3 | 1 |
+-----------+-----------+
思路
第一眼看题目又是select + 临时表 + group by。
测试
- 第一次提交
select
player_id, device_id
from Activity
group by player_id
having min(event_date)
评论发现
having子句执行在select 之后,因此having中的字段必须是在select子句中的,event_date没有再select子句里,所以不行。
测试：
select
player_id, device_id, event_date
from Activity
group by player_id
having min(event_date)
输入:
{"headers":{"Activity":["player_id","device_id","event_date","games_played"]},"rows":{"Activity":[[1,2,"2016-03-01",5],[1,2,"2016-05-02",6],[2,3,"2017-06-25",1],[3,1,"2016-03-02",0],[3,4,"2018-07-03",5]]}}
输出
{"headers": ["player_id", "device_id", "event_date"], "values": [[1, 2, "2016-03-01"], [2, 3, "2017-06-25"], [3, 1, "2016-03-02"]]}
预期结果
{"headers":["player_id","device_id"],"values":[[1,2],[2,3],[3,1]]}
结果确实这样。
- 第二次提交
还是看了答案
select
player_id, device_id
from activity
where (player_id, event_date) in (
select player_id, min(event_date)
from activity
group by player_id
)
总结
having子句执行在select 之后,因此having中的字段必须是在select子句中
来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/game-play-analysis-ii
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