您如何找到每个用户的第一个事件和该事件的时间？

Question

user	timestamp	event
1	2021-2-10	answered
1	2021-2-15	answered
2	2021-2-11	answered
2	2021-2-14	answered
2	2021-2-12	unanswered
3	2021-2-16	next question
3	2021-2-13	next question
4	2021-2-12	next question
4	2021-2-17	answered

Answer 1

你可以考虑

查询 1. 使用 ROW_NUMBER 等窗口函数对行进行排序和过滤
查询 2. 使用查找最早开始日期的聚合查询过滤您的记录

请参阅下面的工作小提琴，其中一种方法可以完成上述建议的方法。

查询 #1

SELECT
    user,
    timestamp,
    event
FROM (
    SELECT
        *,
        ROW_NUMBER() OVER (PARTITION BY user ORDER BY timestamp) rn
    FROM
        my_table
) t
WHERE
    rn=1;

user	timestamp	event
1	2021-02-10	answered
2	2021-02-11	answered
3	2021-02-13	next question
4	2021-02-12	next question

---

查询 #2

SELECT
    t1.user,
    t1.timestamp,
    t1.event
FROM 
    my_table t1
INNER JOIN
    (
        SELECT
            user,
            MIN(timestamp) as min_timestamp
        FROM
            my_table
        GROUP BY
            user
    ) t2 ON t1.user=t2.user AND
            t1.timestamp=t2.min_timestamp;

user	timestamp	event
1	2021-02-10	answered
2	2021-02-11	answered
3	2021-02-13	next question
4	2021-02-12	next question

---

View on DB Fiddle

让我知道这是否适合你。

Answer 2

• 首先，您将根据时间戳和 id 为每一行创建排名
• 然后我们只选择rank = 1

WITH data as (

SELECT 
*,
ROW_NUMBER () OVER(PARTITION BY USER ORDER BY TIMESTAMP) as rank_
FROM my_table
)

SELECT * from data where rank_ = 1

Answer 3

这应该适用于 MySQL 5.6：

select * from (
  select * from events
  order by user, timestamp
) a
group by user
having timestamp = min(timestamp);

编辑
MySQL 8.0 版本：

select e1.user, e1.timestamp, event from (
  select user, min(timestamp) timestamp
  from events
  group by user
) e1
  left join (select * from events) e2
  on e2.user = e1.user
  and e2.timestamp = e1.timestamp

DB Fiddle