批量更新

有如下两个表：
table1:
            field1             field2
            101                   100
            102                   200
            103                   300

table2:  
            field1             field2
            101                   111
            102                   222

如果运行如下语句：
update   table1   set   field2=(select   max(field2)   from   table2
                                                    where   table1.field1=table2.field1)
where   exists(select   field2   from   table2
                                                    where   table1.field1=table2.field1);


update xmstc.student s  set
s.city =(
select a1.areaname from xmstc.area a1 where a1.areaid = (
select  a2.parentid as id2  from gk.area a2 where a2.areaname = du.city  and a2.depth =3
)
)  where exists (
select areaname from  xmstc.area a3 where a3.city =  a3.areaname and a3.depth =3

)