SQL中Merge用法详解

create table a (id_ integer,count_ integer);
insert into a values(1,3);
insert into a values(3,6);
create table b (id_ integer,count_ integer);
insert into b values(1,7);
insert into b values(2,4);
MERGE INTO a
 USING b
 ON (a.id_ = b.id_)
WHEN MATCHED THEN
 UPDATE SET count_ = b.count_+a.count_ /* 注意指名count_属于的表 */
WHEN NOT MATCHED THEN
 INSERT VALUES (b.id_,b.count_);
mit;
select * from a;

create table test1 
(id int,name varchar(20)) 
go 
create table test2 
(id int,name varchar(20)) 
go 
insert into test1(id,name) 
values(1,'boyi55'),(2,'51cto'),(3,'bbs'),(4,'fengjicai'),(5,'alis') 
insert into test2(id,name) 
values(1,'boyi'),(2,'51cto')

merge test2 t --要更新的目标表 
using test1 s --源表 
on t.id=s.id --更新条件（即主键） 
when matched --如果主键匹配，更新 
then update set t.name=s.name 
when not matched then insert values(id,name);--目标主未知主键，插入。此语句必须以分号结束

select a.id,a.name as name_1,b.name as name_2 from test1 as a,test2 as b 
where a.id=b.id