ORACLE 兩表關聯更新三種方式

建立以下表數據

select * from t1 ;

select * from t2;

現需求：參照T2表，修改T1表，修改條件爲兩表的fname列內容一致。

方式1，update

常見陷阱：

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

執行後T1結果以下：

有一行原有值，被更新成空值了。

正確寫法：

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：內聯視圖更新

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;