3种通用分页SQL的比较
多次top倒腾法、【改进版】多次top倒腾法、row_number()法
【改进版】多次top倒腾：倒腾时仅仅使用关键字字段，不再是*，这样io会少很多
实测结果也的确是快了很多！
（如果row_number()法也这样改进，不知道能快多少）
declare @top int,@skip int,@dt datetime
set @top=20
set @skip=5000000
set nocount on
print 'top='+cast(@top as varchar(20))
print 'skip='+cast(@skip as varchar(20))
set @dt=getdate()
--多次top倒腾法
select
* from (
select top(@top)
*
from (
select top(@skip+@top)
*
from tbtestitem
order by fid
) a
order by fid desc
) a
order by fid
print datediff(ms,@dt,getdate())
set @dt=getdate()
--【改进版】多次top倒腾法
select b.* from (
select top(@top)
fid
from (
select top(@skip+@top)
fid
from tbtestitem
order by fid
) a
order by fid desc
) a
left join tbtestitem b on a.fid=b.fid
order by a.fid
print datediff(ms,@dt,getdate())
set @dt=getdate()
--row_number()法
select * from (
select
ROW_NUMBER() Over(order by fid) fo,
*
from tbtestitem
) a
where fo>@skip and fo<=@skip+@top
order by fid
print datediff(ms,@dt,getdate())
set @dt=getdate()
--【改进版】row_number()法
select b.* from (
select * from (
select
ROW_NUMBER() Over(order by fid) fo,fid
from tbtestitem
) a
where fo>@skip and fo<=@skip+@top
) a
left join tbtestitem b on a.fid=b.fid
order by b.fid
print datediff(ms,@dt,getdate())
看执行计划，多次top倒腾法、row_number()法 是一样的开销，
【改进版】多次top倒腾法、row_number()法 比，则前者开销为0！
但是实际情况，跳过的记录数越多，top倒腾的就慢得越厉害
再祥林嫂一句：如果t-sql支持select skip 10000 top 20 * from ...，就好了
结果：先多次top倒腾，中【改进版】多次top倒腾，后row_number，单位:ms
top=20
skip=1000
0
0
16
top=20
skip=10000
46
0
33
top=20
skip=100000
673
126
200
top=20
skip=1000000
10046
1720
1906
top=20
skip=2000000
21176
4063
3673
top=20
skip=5000000
65010
10660
8423
top=20
skip=10000000
159156
23833
17536
4个sql的结果：
top=20
skip=5000000
64616
11066
6603
2740
top=20
skip=1000000
9266
1730
1406
546