求SQL查询语句。在线等

[thhui]

刷卡表 a：

a_id checkdate checktime
-----------------------------------
1 2008-02-01 08:00:00
1 2008-02-01 17:00:00
1 2008-02-03 08:00:00
1 2008-02-03 13:00:00
1 2008-02-03 17:00:00
1 2008-02-04 17:00:00
2 2008-02-11 08:00:00
2 2008-02-11 17:00:00
2 2008-02-13 08:00:00
3 2008-02-23 13:00:00
4 2008-02-03 17:00:00
4 2008-02-04 17:00:00


a_id唯一，现在要得出每个人这个月有多少天打卡的统计表
如： a_id=2这个人，刷卡记录表有3条记录，但是只有11号和13号两天。
那么得出的结果要是这样的 ：

a_id 天数
-------------------------
2 2




请指教！！！！！！！
谢谢

[dawugui]

select a_id , count(*) 天数 from (select distinct a_id , checkdate from a) t group by a_id

[青锋-SS]

select a_id,sun(1) as 天数
from (select a_id,checkdate from a group by a_id,checkdate) t
group by a_id

[wzy_love_sly]

select a_id, count(distinct convert(varchar(10),checkdate,120)) from a
group by a_id

[青锋-SS]

破网通,搞的俺慢了一步

[thhui]

asdadadadasdas

[dawugui]

create table A(a_id int, checkdate varchar(10) , checktime varchar(10) )
insert into A values(1, '2008-02-01', '08:00:00') 
insert into A values(1, '2008-02-01', '17:00:00') 
insert into A values(1, '2008-02-03', '08:00:00') 
insert into A values(1, '2008-02-03', '13:00:00') 
insert into A values(1, '2008-02-03', '17:00:00') 
insert into A values(1, '2008-02-04', '17:00:00') 
insert into A values(2, '2008-02-11', '08:00:00') 
insert into A values(2, '2008-02-11', '17:00:00') 
insert into A values(2, '2008-02-13', '08:00:00') 
insert into A values(3, '2008-02-23', '13:00:00') 
insert into A values(4, '2008-02-03', '17:00:00') 
insert into A values(4, '2008-02-04', '17:00:00') 
go

select a_id , count(distinct checkdate) 天数 from A group by a_id order by a_id
/*
a_id        天数          
----------- ----------- 
1           3
2           2
3           1
4           2

（所影响的行数为 4 行）
*/

select a_id , count(*) 天数 from (select distinct a_id , checkdate from A) t group by a_id order by a_id
/*
a_id        天数          
----------- ----------- 
1           3
2           2
3           1
4           2

（所影响的行数为 4 行）
*/

drop table A

[一品梅]

select a_id , count(*) 天数 from (select distinct a_id , checkdate from A) t group by a_id order by a_id
在这里,distinct根据查询所有列找唯一.

[lhsxsh]

select a_id,sun(1) as 天数
from (select a_id,checkdate from a group by a_id,checkdate) t
group by a_id

[heshengfen123]

select a_id,count(distinct checkdate) 天数 from tt_a group by a_id