Mysql中使用Update From语句

记录一下mysql中使用Update from 语句更新字段值：

场景是国家行政区划的数据表，字段内容包括：

应用场景中不想使用级联选择，选中下级节点，比如东城区时，直接显示北京-北京市-东城区，因此打算给数据表增加一个字段fullname， 显示完整名称：

--更新第一级省的fullname
update tb_conf_area set fullname=name where LEVEL =1

--更新第二级市的fullname
update tb_conf_area a inner join (select a.*, concat(b.fullname,'-',a.name)  as parentname from tb_conf_area a inner join tb_conf_area b on a.pid=b.oid
where a.level=2) b
on a.oid=b.OID 
set a.fullname=b.parentname
where a.`LEVEL` =2

--更新第三级区的fullname
update tb_conf_area a inner join (select a.*, concat(b.fullname,'-',a.name)  as parentname from tb_conf_area a inner join tb_conf_area b on a.pid=b.oid
where a.level=3) b
on a.oid=b.OID 
set a.fullname=b.parentname
where a.`LEVEL` =3

--更新第四级街道的fullname
update tb_conf_area a inner join (select a.*, concat(b.fullname,'-',a.name)  as parentname from tb_conf_area a inner join tb_conf_area b on a.pid=b.oid
where a.level=4) b
on a.oid=b.OID 
set a.fullname=b.parentname
where a.`LEVEL` =4