如何使用 SQL（基于时间戳）中的其他值更新表列的值？

Question

I need to update empty values in a table with values presents in another table. Shortly these values are ids of groups, and I need to pass these groupids in all events of my users to recognize in which group the user held this event. Example:

Inputs:

Table A:

event	timestamp	groupid	userid
created	2021-03-09T09:58:17.198362522Z		c98
updated	2021-03-09T09:59:17.198362522Z		c98
created	2021-03-09T09:46:17.198362522Z		a32
updated	2021-03-09T10:20:17.198362522Z		c98
updated	2021-03-09T10:22:17.198362522Z		c98
created	2021-03-09T09:58:17.198362522Z		a32
created	2021-03-09T10:40:17.198362522Z		c98

Table B:

groupid	timestamp	userid
f13	2021-03-09T09:58:17.198362522Z	c98
f14	2021-03-09T10:15:17.198362522Z	c98
ad8	2021-03-09T09:45:00.198362522Z	a32
ad9	2021-03-09T09:58:17.198362522Z	a32

Desired Output:

Table A:

event	timestamp	groupid	userid
created	2021-03-09T09:58:17.198362522Z	f13	c98
updated	2021-03-09T09:59:17.198362522Z	f13	c98
created	2021-03-09T09:46:17.198362522Z	ad8	a32
updated	2021-03-09T10:20:17.198362522Z	f14	c98
updated	2021-03-09T10:22:17.198362522Z	f14	c98
created	2021-03-09T09:59:17.198362522Z	ad9	a32
created	2021-03-09T10:40:17.198362522Z	f14	c98

Answer 1

isn't it just a simple join?

update table1 a
set groupid = (select groupid from table2 b
                where a.userid = b.userid
                and a.timestamp >= b.timestamp
                order by b.timestamp desc
                limit 1
              )
where a.groupid id null