原文章出处（http://blog.csdn.net/lichkui/article/details/4306299）
MERGE语句是Oracle9i新增的语法，用来合并UPDATE和INSERT语句。通过MERGE语句，根据一张表或子查询的连接条件对另外一张表进行查询，连接条件匹配上的进行UPDATE，无法匹配的执行INSERT。这个语法仅需要一次全表扫描就完成了全部工作，执行效率要高于INSERT＋UPDATE。
//表1
create table subs(msid number(9),
ms_type char(1),
areacode number(3)
);
//表2
create table acct(msid number(9),
bill_month number(6),
areacode number(3),
fee number(8,2) default 0.00);
//测试数据
insert into subs values(905310001,0,531);
insert into subs values(905320001,1,532);
insert into subs values(905330001,2,533);
commit;
一.下面先演示一下merge的基本功能
1) matched 和not matched clauses 同时使用
merge into acct a
using subs b on (a.msid=b.msid)
when MATCHED then
update set a.areacode=b.areacode
when NOT MATCHED then
insert(msid,bill_month,areacode)
values(b.msid,'200702',b.areacode);
2) 只有not matched clause,也就是只插入不更新
merge into acct a
using subs b on (a.msid=b.msid)
when NOT MATCHED then
insert(msid,bill_month,areacode)
values(b.msid,'200702',b.areacode);
3) 只有matched clause, 也就是只更新不插入
merge into acct a
using subs b on (a.msid=b.msid)
when MATCHED then
update set a.areacode=b.areacode
二.10g中增强一：条件操作
1) matched 和not matched clauses 同时使用
merge into acct a
using subs b on (a.msid=b.msid)
when MATCHED then
update set a.areacode=b.areacode
where b.ms_type=0
when NOT MATCHED then
insert(msid,bill_month,areacode)
values(b.msid,'200702',b.areacode)
where b.ms_type=0;
2) 只有not matched clause,也就是只插入不更新
merge into acct a
using subs b on (a.msid=b.msid)
when NOT MATCHED then
insert(msid,bill_month,areacode)
values(b.msid,'200702',b.areacode)
where b.ms_type=0;
3) 只有matched clause, 也就是只更新不插入
merge into acct a
using subs b on (a.msid=b.msid)
when MATCHED then
update set a.areacode=b.areacode
where b.ms_type=0;
三.10g中增强二：删除操作
merge into acct a
using subs b on (a.msid=b.msid)
when MATCHED then
update set a.areacode=b.areacode
delete where (b.ms_type!=0);
注意:
1.MERGE语句的UPDATE不能修改用于连接的列，否则会报错(on 后面的条件列就是联接)
2.using 后面可以是(SELECT msid ,areacode FROM subs GROUP by msid )