SQL:merge 用法 【SQL Server 2008开始支持merge】

SQL:merge 用法  

merge主要用于两表之间的关联操作

oracle中 merge:

从oracle 9i开始支持merge用法，10g有了完善
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_);commit;
 select * from a;

结果：

    id_   count_

    1        10

    3          6

    2          4

SQL Server 2008开始支持merge:

有两张结构一致的表：test1,test2

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')

将test1同步到test2中，没有的数据进行插入，已有数据进行更新

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

运行以下查询查看更新结果

select a.id,a.name as name_1,b.name as name_2  from test1 as a,test2 as b 
 where a.id=b.idid          name_1               name_2 
 ----------- -------------------- -------------------- 
 1           boyi55               boyi55 
 2           51cto                51cto 
 3           bbs                  bbs 
 4           fengjicai            fengjicai 
 5           alis                 alis