解析SQLServer2005的Top功能

set nocount on
use tempdb
go
if (object_id ('tb' ) is not null )
    drop table tb
go
create table tb (id int identity (1 , 1 ), name varchar (10 ), tag int default 0 )
insert into tb (name ) select 'a'
insert into tb (name ) select 'b'
insert into tb (name ) select 'c'
insert into tb (name ) select 'd'
insert into tb (name ) select 'e'
/*--更新前两行
id          name       tag
----------- ---------- -----------
1           a          1
2           b          1
3           c          0
4           d          0
5           e          0
*/
update top (2 )  tb set tag = 1
select * from tb
/*--更新后两行
id          name       tag
----------- ---------- -----------
1           a          1
2           b          1
3           c          0
4           d          1
5           e          1
*/
;with t as
(
    select top (2 ) * from tb order by id desc
)
update   t set tag = 1
select * from tb
/*--删除前两行
id          name       tag
----------- ---------- -----------
3           c          0
4           d          1
5           e          1
*/
delete top (2 ) from tb
select * from tb
/*--删除后两行
id          name       tag
----------- ---------- -----------
3           c          0
*/
;with t as
(
    select top (2 ) * from tb order by id desc
)
delete from   t
select * from tb
set nocount off