ORACLE 两表关联更新三种方式

创建如下表数据

select * from t1 ;

select * from t2;

现需求：参照T2表，修改T1表，修改条件为两表的fname列内容一致。

方式1，update

常见陷阱：

UPDATE T1 
SET T1.FMONEY = (select T2.FMONEY from t2 where T2.FNAME = T1.FNAME)

执行后T1结果如下：

有一行原有值，被更新成空值了。

正确写法：

UPDATE T1 
SET T1.FMONEY = (select T2.FMONEY from t2 where T2.FNAME = T1.FNAME)
WHERE EXISTS(SELECT 1 FROM T2 WHERE T2.FNAME = T1.FNAME);

方式2：内联视图更新

UPDATE (
select t1.fmoney  fmoney1,t2.fmoney  fmoney2 from t1,t2 where t1.fname = t2.fname
)t
set fmoney1 =fmoney2;

方式3：merge更新

merge into t1
using (select t2.fname,t2.fmoney from t2) t
on (t.fname = t1.fname)
when matched then 
  update  set t1.fmoney = t.fmoney;