所有人都知道select top 的用法，但很多人还不知道update top 和 delete top 怎么用。以往的做法是set rowcount来指定，其实SQL2005中对于Top语句的增强除了参数化之外还包括对update和delete的支持，但可惜的是还不支持自定义的order by列。如果要自定义派序列可以借助CTE.对于CTE的任何更改都会影响到原始表。 我们看下面的测试代码。
复制代码 代码如下:
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
