merge into 常用于联表更新

格式：

merge into ...

using (...)

on (...)

when matched then ...

when not matched then...

例如：A和B 匹配时更新，不匹配则插入

merge into A a

using (select * from B) b

on (a.id=b.id)

when matched then 

update set a.name=b.name

when not matched then

insert (id,name)=(b.id,b.name)

注意：update 后没有表名

Insert 后没有into 表名