疯子，你搞的真复杂。。

declare @date1 datetime,@date2 datetime
set @date1='2008-01-3'
set @date2='2008-02-19'

select datediff(dd,dateadd(dd,-6,dateadd(dd,7-datepart(dw,@date1),@date1)),
dateadd(dd,-6,dateadd(dd,7-datepart(dw,@date2),@date2)))/7

------解决方案--------------------
SQL code
如果是2000，返回天数
select count(1)
from  
(select 0 as id
union all select 1 as id ) t1,
(select 0 as id
union all select 2 as id ) t2,
(select 0 as id
union all select 4 as id ) t3,
(select 0 as id
union all select 8 as id ) t4,
(select 0 as id
union all select 16 as id ) t5,
(select 0 as id
union all select 32 as id ) t6,
(select 0 as id
union all select 64 as id ) t7,
(select 0 as id
union all select 128 as id ) t8,
(select 0 as id
union all select 256 as id ) t9,
(select 0 as id
union all select 512 as id ) t10 
where t1.id+t2.id+t3.id+t4.id+t5.id+t6.ID+t7.id+t8.id+t9.id+t10.id<= datediff(day,'2008-01-01','2008-04-01') 
   and (DATEPART(Weekday,dateadd(day,t1.id+t2.id+t3.id+t4.id+t5.id+t6.ID+t7.id+t8.id+t9.id+t10.id,'2008-01-01'))+@@DATEFIRST-1)%7 IN (0,6)