下面是另一种解决方案：

select time_out, time_in,
       (select employee_name from table_employee where emp_no = tb.tagged_by) tagged_by,
       (select employee_name from table_employee where emp_no = tb.untagged_by) untagged_by,
from table_breaktime tb

您可能想看看join的标准mysql文档

select timeout, 
       timein, 
       taggedby.employee_name tagged_by,
       untaggedby.employee_name untagged_by 
  from table_breaktime tb
  JOIN table_employee taggedby on taggedby.emp_no = tb.tagged_by
  JOIN table_employee untaggedbyon untaggedby.emp_no = tb.untagged_by

我们在列上两次加入employee表 tagged_by 以及 untagged_by 从table上 table_breaktime . 单独获取员工姓名