本文主要向大家介紹了Oracle數據庫之oracle update set select from 關聯更新,通過具體的內容向大家展現,希望對大家學習Oracle數據庫有所幫助。
工作中有個需求,現在新表中有一些數據跟老表的基本一樣,這樣只需要把老表中數據搬到新表中就可以了,同時把不同的字段修改下數據即可,在修改字段時發 現,需要指定一個條件,比如主鍵id,來修改某條記錄,這樣一條一條修改效率太低了,有沒有批量操作的方式 呢?SQL>select * from wwn2;
TOWN ID
-------------------- ----------
222 222
111 111
ww‘jj 111
llll 1111
dddd 2222
lllldf 111
lllldf 111
dsafdf 111
3435 111
ljjjjj 222
dsafdf 111
3435 111
ljjjjj 222
SQL> select * from wwm5;
TOWN ID
-------------------- ----------
lllldf 111
test 9984
SQL> select wwm2.* from wwm2,wwm5 where wwm2.id=wwm5.id
TOWN ID
-------------------- ----------
111 111
ww‘jj 111
lllldf 111
lllldf 111
dsafdf 111
3435 111
dsafdf 111
3435 111
8 rows selected.
--需要更新8條數據是正確的
下面是一個錯誤的做法:
SQL> update wwm2 set wwm2.town=(select wwm5.town from wwm5 where wwm5.id=wwm2.id)
13 rows updated.
SQL> select * from wwm2;
TOWN ID
-------------------- ----------
222
lllldf 111
lllldf 111
1111
2222
lllldf 111
lllldf 111
lllldf 111
lllldf 111
222
lllldf 111
lllldf 111
222
13 rows selected.
--可以看到13條記錄被更新,符合條件的更新正確,不符合條件的也更新爲NULL.以下是正確的方法
解決方法:
方法一:
SQL> update wwm2
2 set town=(select town from wwm5 where wwm5.id=wwm2.id)
3 where id=(select wwm5.id from wwm5 where wwm5.id=wwm2.id)
方法二:
SQL> update wwm2
set town=(select town from wwm5 where wwm5.id=wwm2.id)
where exists (select 1 from wwm5 where wwm5.id=wwm2.id)
方法三:
1 declare
2 cursor cur_wwm is select town,id from wwm5;
3 begin
4 for my_wwm in cur_wwm loop
5 update wwm2 set town=my_wwm.town
6 where id=my_wwm.id;
7 end loop;
8 end;
說 明:如果select 子句可以返回多行記錄,但返回適合where條件的記錄只能是唯一的,否則將會報返回單行的select子句返回多行的錯誤,因爲 update只能跟據此處的where子句(內層where)進行相應記錄的匹配更新,一次只能是一條。實際使用的sql爲:
update table1 s set s.yesterday = (select yesterday from table1_BACK sb where sb.tagname = s.tagname and rownum = 1) where s.tagname = (select tagname from table1_BACK sb where sb.tagname = s.tagname);update table1 s set s.yesterday = (select yesterday from table1_BACK sb where sb.tagname = s.tagname and rownum = 1) where exists (select 1 from table1_BACK sb where sb.tagname = s.tagname);
轉自:http://m.zhizuobiao.com/oracle/oracle-18091000132/