filed函数中，我如何通过filed获取子对象里面的实体类或值

我通过sql语句
select letter.l_number,letter.center_receivedate,letter.department_receivedate,letter.l_occurrencedate,letter.l_u_name,letter.business_name,
mechanism_name.mn_name
sql语句运行没问题后台可以取到数据

如何获取mechanism_name.mn_name这个值赋值到最后一行


var columns=[
    {field:'l_number', width: 200,title:'编号'},
    {field:'center_receivedate', width: 200,title:'日期'},
    {field:'department_receivedate', width: 200,title:'客接受日期'},
    {field:'l_occurrencedate', width: 200,title:'发生日期'},
    {field:'l_u_name', width: 200,title:'名称'},
    {field:'business_name', width: 200,title:'名称'},
    {field:'business_name', width: 200,title:'企业'},
  {field:'', width: 80,title:'名称'},

搞不懂你在说啥

返回数据是什么，前端就用什么，都是json格式的

{field:'mn_name', width: 80,title:'名称'},