假设您指的是数据库用户以外的其他类型的用户（例如“注册用户”），则触发器可能是解决您的问题的方法。有两个触发器，一个在插入时触发，一个在更新时触发，您可以modified_at使用自定义代码指定-
column的值，例如select user_id from ... where ...

请检查以下示例代码，这些示例代码应直接回答您的问题；希望它能解决您的问题。否则，请给我们更多信息/更多背景信息。

DELIMITER |

drop table if exists sometable
|
CREATE TABLE `sometable` (
  `somecolumn` int(11) DEFAULT NULL,
  `modified_by` int(11) DEFAULT NULL
)
|
drop table if exists registered_user
|
CREATE TABLE registered_user (
  user_id integer primary key,
  name varchar(50)
)
|
drop trigger if exists sometable_inserted
|
drop trigger if exists sometable_modified
|
CREATE TRIGGER sometable_inserted BEFORE INSERT ON sometable
FOR EACH ROW
BEGIN
SET new.modified_by := (select user_id from registered_user where name=@name);
END;
|
CREATE TRIGGER sometable_modified BEFORE UPDATE ON sometable
FOR EACH ROW
BEGIN
SET new.modified_by := (select user_id from registered_user where name=@name);
END;
|

DELIMITER ;

insert into registered_user values (5, 'joe');
insert into registered_user values (6, 'sam');

set @name='sam';
insert into sometable(somecolumn) values (1);
insert into sometable(somecolumn) values (2);
set @name='joe';
update sometable set somecolumn = 3 where somecolumn = 2;