oracle 中关于update select 语句的问题

是这样的，我已经使用select 连接多表取得想要更新的记录集，共有139条记录，FAssGrpID值都是'ZZW0XxLMQjqiyV/6c9PO2kGKbLs='
现在想在这查出的139条记录中更新 FAssGrpID值为其它值，在oracel中应该怎么写语句呢？？求助呀~~
 
SQL code

select tgv.fid,tgv.fbookeddate,tgv.fnumber,tgve.flocalamount,tgve.fid,tgve.faccountid,tgvar.fid,tgvar.fentryid,tgvar.fassgrpid,tgvar.fbillid  from T_GL_VoucherAssistRecord tgvar, T_GL_Voucher tgv,T_GL_VoucherEntry tgve where tgvar.FAssGrpID='ZZW0XxLMQjqiyV/6c9PO2kGKbLs=' 
and tgvar.fbillid=tgv.fid and tgv.fcompanyid='X6LYi/UfSGuuUA9ZNwxJasznrtQ='
and tgvar.fentryid=tgve.fid and tgve.faccountid='TIwPYRKyRUy4gNse9h1Z+p2pmCY=' order by fbookeddate

SQL code

 update T_GL_VoucherAssistRecord t 
 set t.FAssGrpID=? -- 更新 FAssGrpID值为其它值
 where (t.fid,t.fentryid,t.fassgrpid,t.fbillid) 
 in (
       select 
              tgvar.fid,
              tgvar.fentryid,
              tgvar.fassgrpid,
              tgvar.fbillid
       from T_GL_VoucherAssistRecord tgvar,
            T_GL_Voucher             tgv,
            T_GL_VoucherEntry        tgve
       where tgvar.FAssGrpID = 'ZZW0XxLMQjqiyV/6c9PO2kGKbLs='
       and tgvar.fbillid = tgv.fid
       and tgv.fcompanyid = 'X6LYi/UfSGuuUA9ZNwxJasznrtQ='
       and tgvar.fentryid = tgve.fid
       and tgve.faccountid = 'TIwPYRKyRUy4gNse9h1Z+p2pmCY='
 )

请参考：
SQL code

UPDATE T_GL_VoucherAssistRecord 
SET FAssGrpID = 更新后的值
WHERE EXISTS
(select 1  
 from T_GL_VoucherAssistRecord tgvar, T_GL_Voucher tgv,T_GL_VoucherEntry tgve 
 where tgvar.FAssGrpID='ZZW0XxLMQjqiyV/6c9PO2kGKbLs=' 
 and tgvar.fbillid=tgv.fid 
 and tgv.fcompanyid='X6LYi/UfSGuuUA9ZNwxJasznrtQ='
 and tgvar.fentryid=tgve.fid 
 and tgve.faccountid='TIwPYRKyRUy4gNse9h1Z+p2pmCY=');