Sql server with as update用法

create table t1
( id int,[names] varchar(100))

create table t2
( id int,[names] varchar(100))

insert into t1 values(1,'t1');
insert into t1 values(2,'t2');
insert into t1 values(3,'t3');

insert into t2 values(1,'ttt1');

with temp(id,names) as
(
select id,names from t1
)

Merge into temp as a
Using t2 as b on a.id=b.id
when MATCHED THEN
Update SET a.names = b.names;