SQL中表变量的使用，代替IN的操作（效果差不多，有时IN可能会比表变量的好一点点：数据量10000000）

CREATE TABLE t_userinfo(
userid int identity(1,1) primary key nonclustered,
nick varchar(50) not null default '',
classid int not null default 0,
writetime datetime not null default getdate())
go
-- 建索引
create clustered index ix_userinfo_classid on t_userinfo(classid)
go
-- 插入数据
declare @i int
declare @k int
declare @nick varchar(10)
set @i = 1
while @i<10000000
begin
set @k = @i % 10
set @nick = convert(varchar,@i)
insert into t_userinfo(nick,classid,writetime) values(@nick,@k,getdate())
set @i = @i + 1
end

declare @tempTb table(id int)
insert @tempTb
select 1 union all
select 2 union all
select 3 union all
select 4 union all
select 5;
--select * from @tempTb

select a.userid,b.nick,b.classid,b.writetime from
(
select top 20 a.userid from
(
select top 1000000 userid from t_userinfo inner join @tempTb on classid=id
where  writetime>'2013-03-05 17:49:33.247'
order by userid asc
) a order by a.userid desc
)a inner join t_userinfo b on a.userid = b.userid
order by a.userid asc

select a.userid,b.nick,b.classid,b.writetime from
(
select top 20 a.userid from
(
select top 1000000 userid from t_userinfo
where  classid =1 and writetime>'2013-03-05 17:49:33.247'
order by userid asc
union all
select top 1000000 userid from t_userinfo
where  classid =2 and writetime>'2013-03-05 17:49:33.247'
order by userid asc
union all
select top 1000000 userid from t_userinfo
where  classid =3 and writetime>'2013-03-05 17:49:33.247'
order by userid asc
union all
select top 1000000 userid from t_userinfo
where  classid =4 and writetime>'2013-03-05 17:49:33.247'
order by userid asc
union all
select top 1000000 userid from t_userinfo
where  classid =5 and writetime>'2013-03-05 17:49:33.247'
order by userid asc
) a order by a.userid desc
)a inner join t_userinfo b on a.userid = b.userid
order by a.userid asc

select a.userid,b.nick,b.classid,b.writetime from
(
select top 20 a.userid from
(
select top 1000000 userid from t_userinfo
where  classid =1 and writetime>'2013-03-05 17:49:33.247'
order by userid asc
) a order by a.userid desc
)a inner join t_userinfo b on a.userid = b.userid
order by a.userid asc

select a.userid,b.nick,b.classid,b.writetime from
(
select top 20 a.userid from
(
select top 1000000 userid from t_userinfo
where  classid =2 and writetime>'2013-03-05 17:49:33.247'
order by userid asc
) a order by a.userid desc
)a inner join t_userinfo b on a.userid = b.userid
order by a.userid asc

select a.userid,b.nick,b.classid,b.writetime from
(
select top 20 a.userid from
(
select top 1000000 userid from t_userinfo
where  classid =3 and writetime>'2013-03-05 17:49:33.247'
order by userid asc
) a order by a.userid desc
)a inner join t_userinfo b on a.userid = b.userid
order by a.userid asc
select a.userid,b.nick,b.classid,b.writetime from
(
select top 20 a.userid from
(
select top 1000000 userid from t_userinfo
where  classid =4 and writetime>'2013-03-05 17:49:33.247'
order by userid asc
) a order by a.userid desc
)a inner join t_userinfo b on a.userid = b.userid
order by a.userid asc
select a.userid,b.nick,b.classid,b.writetime from
(
select top 20 a.userid from
(
select top 1000000 userid from t_userinfo
where  classid =5 and writetime>'2013-03-05 17:49:33.247'
order by userid asc
) a order by a.userid desc
)a inner join t_userinfo b on a.userid = b.userid
order by a.userid asc

set statistics profile on
select a.userid,b.nick,b.classid,b.writetime from
(
select top 20 a.userid from
(
select top 1000000 userid from t_userinfo
where  classid in(1,2,3,4,5) and writetime>'2013-03-05 17:49:33.247'
order by userid asc
) a order by a.userid desc
)a inner join t_userinfo b on a.userid = b.userid
order by a.userid asc