如果您使用的是早期版本的mysql，它不支持分析函数：
（这应该等同于@used\u by \u already的另一个答案）

SELECT 
  t2.Id, 
  t2.userName, 
  COALESCE(t2.Browser, t2.other_Browser), 
  COALESCE(t2.Platform, t2.other_Platform),
  t2.TS, 
  t2.other_TS
from (

SELECT 
  t.*,
  IF (t.Id = @prev_id, @rankk:=@rankk+1, @rankk:=0) as rankk,
  @prev_id := t.Id
from (
  select 
    a.Id, a.userName, a.Browser , a.Platform, a.TS, 
    b.Id as other_Id, b.Browser as other_Browser , b.Platform as other_Platform, b.TS as other_TS,
    ABS(TIMESTAMPDIFF(SECOND, a.TS, b.TS)) as time_diff
  from mytable a join mytable b on a.userName = b.userName and a.Id <> b.Id
  order by a.Id, ABS(TIMESTAMPDIFF(SECOND, a.TS, b.TS)))
  t join (select @prev_Id:=NULL, @rankk:=0) c
) t2
 WHERE rankk=0

如果您有mysql v8或mariadb，那么 lead() over() ```
CREATE TABLE mytable(
Id INT
,userName VARCHAR(10)
,Browser VARCHAR(9)
,Platform VARCHAR(10)
,TS timestamp
);

INSERT INTO mytable(Id,userName,Browser,Platform,TS) VALUES > > > > > (1,'abc','Firefox',NULL,'2006-10-05 11:55:45');
, (2,'xyz','Chrome',NULL,'2007-10-07 12:34:17');
, (3,'mnp','Safari',NULL,'2008-10-09 08:19:37');
, (4,'abc','Safari',NULL,'2010-10-13 04:28:14')
, (5,'abc',NULL,'Windows','2006-01-01 12:02:45')
, (6,'xyz',NULL,'Linux','2007-01-01 12:01:20')
, (7,'mnp',NULL,'MAC','2008-01-01 12:02:29')
, (8,'abc',NULL,'MAC','2010-03-09 13:06:59')

with cte as (
select

, coalesce(lead(ts) over(order by ts),current_time) nxt
from mytable
)
select
id
, username
, coalesce(browser,(select browser from cte where t.ts between cte.ts and cte.nxt limit 1 )) browser
, coalesce(platform,(select platform from cte where t.ts between cte.ts and cte.nxt limit 1 )) platform
, ts
, nxt
from cte t

id | username | browser | platform | ts | nxt
-: | :------- | :------ | :------- | :------------------ | :------------------
5 | abc | null | Windows | 2006-01-01 12:02:45 | 2006-10-05 11:55:45
1 | abc | Firefox | Windows | 2006-10-05 11:55:45 | 2007-01-01 12:01:20
6 | xyz | Firefox | Linux | 2007-01-01 12:01:20 | 2007-10-07 12:34:17
2 | xyz | Chrome | Linux | 2007-10-07 12:34:17 | 2008-01-01 12:02:29
7 | mnp | Chrome | MAC | 2008-01-01 12:02:29 | 2008-10-09 08:19:37
3 | mnp | Safari | MAC | 2008-10-09 08:19:37 | 2010-03-09 13:06:59
8 | abc | Safari | MAC | 2010-03-09 13:06:59 | 2010-10-13 04:28:14
4 | abc | Safari | MAC | 2010-10-13 04:28:14 | 2018-10-02 08:11:44

db<>在这里摆弄