oracle中merge into语句详解_oracle merge into 删除

一、merge into语句的语法。

MERGE INTO schema. table alias
USING { schema. table | views | query} alias
ON {(condition) }
WHEN MATCHED THEN
  UPDATE SET {clause}
WHEN NOT MATCHED THEN
  INSERT VALUES {clause};
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–解析
INTO 子句
用于指定你所update或者Insert目的表。
USING 子句
用于指定你要update或者Insert的记录的来源，它可能是一个表，视图，子查询。
ON Clause
用于目的表和源表（视图，子查询）的关联，如果匹配（或存在），则更新，否则插入。
merge_update_clause
用于写update语句
merge_insert_clause
用于写insert语句
二、merge 语句的各种用法练习

创建表及插入记录

create table t_B_info_aa
( id varchar2(20),
  name varchar2(50),
  type varchar2(30),
  price number
);
insert into t_B_info_aa values('01','冰箱','家电',2000);
insert into t_B_info_aa values('02','洗衣机','家电',1500);
insert into t_B_info_aa values('03','热水器','家电',1000);
insert into t_B_info_aa values('04','净水机','家电',1450);
insert into t_B_info_aa values('05','燃气灶','家电',800);
insert into t_B_info_aa values('06','太阳能','家电',1200);
insert into t_B_info_aa values('07','西红柿','食品',1.5);
insert into t_B_info_aa values('08','黄瓜','食品',3);
insert into t_B_info_aa values('09','菠菜','食品',4);
insert into t_B_info_aa values('10','香菇','食品',9);
insert into t_B_info_aa values('11','韭菜','食品',2);
insert into t_B_info_aa values('12','白菜','食品',1.2);
insert into t_B_info_aa values('13','芹菜','食品',2.1);
create table t_B_info_bb
( id varchar2(20),
  type varchar2(50),
  price number
);
insert into t_B_info_bb values('01','家电',2000);
insert into t_B_info_bb values('02','家电',1000);
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1. update和insert同时使用

merge into t_B_info_bb b
using t_B_info_aa a --如果是子查询要用括号括起来
on (a.id = b.id and a.type = b.type) --关联条件要用括号括起来
when matched then
update set b.price = a.price --update 后面直接跟set语句

when not matched then
insert (id, type, price) values (a.id, a.type, a.price) --insert 后面不加into
—这条语句根据t_B_info_aa 更新了t_B_info_bb中的一条记录，插入了11条记录

2)只插入不更新

–处理表中数据，使表中的一条数据发生变化，删掉一部分数据。用来验证只插入不更新的功能

update t_B_info_bb b set b.price=1000 where b.id=‘02’;
delete from t_B_info_bb b where b.type=‘食品’;
–只是去掉了when matched then update语句

merge into t_B_info_bb b
using t_B_info_aa a
on (a.id = b.id and a.type = b.type)
when not matched then
insert (id, type, price) values (a.id, a.type, a.price)
3)只更新不插入

–处理表中数据，删掉一部分数据，用来验证只更新不插入

delete from t_B_info_bb b where b.type=‘食品’;
–只更新不插入，只是去掉了when not matched then insert语句

merge into t_B_info_bb b
using t_B_info_aa a
on (a.id = b.id and a.type = b.type)
when matched then
update set b.price = a.price
三、加入限制条件的操作

变更表中数据，便于练习

update t_B_info_bb b
set b.price = 1000
where b.id=‘02’

delete from t_b_info_bb b where b.id not in (‘01’,‘02’) and b.type=‘家电’

update t_B_info_bb b
set b.price = 8
where b.id=‘10’

delete from t_b_info_bb b where b.id in (‘11’,‘12’,‘13’) and b.type=‘食品’
表中数据

执行merge语句：脚本一和脚本二执行结果相同

脚本一： merge into t_B_info_bb b
using t_B_info_aa a
on (a.id = b.id and a.type = b.type)
when matched then
update set b.price = a.price where a.type = ‘家电’
when not matched then
insert
(id, type, price)
values
(a.id, a.type, a.price) where a.type = ‘家电’;

  ----------------------   
1

脚本二： merge into t_B_info_bb b
using (select a.id, a.type, a.price
from t_B_info_aa a
where a.type = ‘家电’) a
on (a.id = b.id and a.type = b.type)
when matched then
update set b.price = a.price
when not matched then
insert (id, type, price) values (a.id, a.type, a.price);
结果：

上面两个语句是只对类型是家电的语句进行插入和更新

而脚本三是只对家电进行更新，其余的全部进行插入

 merge into t_B_info_bb b
 using t_B_info_aa a
 on (a.id = b.id and a.type = b.type)
 when matched then
   update set b.price = a.price
    where a.type = '家电'
 when not matched then
   insert
     (id, type, price)
   values
     (a.id, a.type, a.price);
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四、加删除操作

update子句后面可以跟delete子句来去掉一些不需要的行

delete只能和update配合，从而达到删除满足where条件的子句的记录

例句：

 merge into t_B_info_bb b
 using t_B_info_aa a
 on (a.id=b.id and a.type = b.type)
 when matched then 
   update set b.price=a.price
   delete where (a.type='食品')
    when not matched then
   insert values (a.id, a.type, a.price) where a.id = '10'
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