--设置星期一是一周的第一天
set datefirst 1
declare @t table ( date datetime )

declare @date datetime
set @date = '2012-03-01'

while ( @date < '2012-03-20' ) 
    begin
        if ( datepart(w, @date) in ( 3, 5 ) ) 
            insert into @t select  @date
        set @date = dateadd(d, 1, @date)
    end

select * from @t
/*
date
-----------------------
2012-03-02 00:00:00.000
2012-03-07 00:00:00.000
2012-03-09 00:00:00.000
2012-03-14 00:00:00.000
2012-03-16 00:00:00.000
*/

------解决方案--------------------
SQL code

--我刚才找的是周三和周五，修正一下
set datefirst 1
declare @t table ( date datetime )

declare @date datetime
set @date = '2012-03-01'

while ( @date < '2012-03-20' ) 
    begin
        if ( datepart(w, @date) in ( 1, 3 ) ) 
            insert into @t select  @date
        set @date = dateadd(d, 1, @date)
    end

select * from @t
/*
date
-----------------------
2012-03-05 00:00:00.000
2012-03-07 00:00:00.000
2012-03-12 00:00:00.000
2012-03-14 00:00:00.000
2012-03-19 00:00:00.000
*/

------解决方案--------------------
SQL code

set datefirst 1
declare @start datetime
declare @end datetime
set @start = '2012-03-01'
set @end = '2012-03-20'
;with ach as
(
    select dateadd(dd,number,@start) date
    from master..spt_values
    where [type] = 'p' and number between 0 and datediff(dd,@start,@end)
)

select *
from ach
where datepart(weekday,date) in (1,3)

------解决方案--------------------
select data from (select dateadd(day,number,'2012-3-1')data from master..spt_values where type='p' and number between 0 and datediff(dd,'2012-3-1','2012-3-20'))
t where datepart(weekday,t.data) in (1,3)