准备工作

drop table demo_t1;
drop table demo_t2;
CREATE TABLE DEMO_T1 
(
  FNAME VARCHAR2(20) 
, FMONEY VARCHAR2(20) 
);
ALTER TABLE demo_t1 ADD PRIMARY KEY(FNAME);
insert into demo_t1 (fname,fmoney) values('A','20');
insert into demo_t1 (fname,fmoney) values('B','30');
CREATE TABLE DEMO_T2
(
  FNAME VARCHAR2(20) 
, FMONEY VARCHAR2(20) 
);
ALTER TABLE demo_t2 ADD PRIMARY KEY(FNAME);
insert into demo_t2 (fname,fmoney) values('C','10');
insert into demo_t2 (fname,fmoney) values('D','20');
insert into demo_t2 (fname,fmoney) values('A','100');

UPDATE DEMO_T1 t1
SET T1.FMONEY = (select T2.FMONEY from DEMO_T2 T2 where T2.FNAME = T1.FNAME)
WHERE EXISTS(SELECT 1 FROM DEMO_T2 T2 WHERE T2.FNAME = T1.FNAME);

如果同时更新多个字段可以参照以下语法：

UPDATE DEMO_T1 t1
SET (字段一,字段二,...) = (select 字段一,字段二,... from DEMO_T2 T2 where T2.FNAME = T1.FNAME)
WHERE EXISTS(SELECT 1 FROM DEMO_T2 T2 WHERE T2.FNAME = T1.FNAME);