按日期进行统计的问题

[BTbug]

各位大大好，小弟碰到个日期统计的问题向大家讨教。
现有如下情况的表单统计表数据：
表单号 起单时间
AOM_0001 2011-10-1 10：20：00
AOM_0002 2011-10-1 12：30：00
AOM_0003 2011-10-2 13：20：00
AOM_0004 2011-10-3 9：30：00
AOM_0005 2011-10-3 15：25：00
AOM_0006 2011-10-3 16：20：00
AOM_0007 2011-10-5 10：20：00
AOM_0008 2011-10-6 11：20：00
AOM_0009 2011-10-6 12：20：00

现在要想得到每天起单的数据量，比如上面的数据能得到：
日期 起单件数
2011-10-1 2
2011-10-2 1
2011-10-3 3
2011-10-5 1
2011-10-6 2

望各为大大提供个简洁有效的SQL语句。

[-晴天]

select convert(varchar(10),起单时间,120)日期,count(*) from tb
group by convert(varchar(10),起单时间,120)

[水族杰纶]

select convert(varchar(10),日期,120),
       count(*)
from tb
group by convert(varchar(10),日期,120)

[-晴天]

CREATE TABLE tb(表单号 varchar(10),起单时间 datetime)
insert into tb select 'AOM_0001','2011-10-1 10:20:00'
insert into tb select 'AOM_0002','2011-10-1 12:30:00'
insert into tb select 'AOM_0003','2011-10-2 13:20:00'
insert into tb select 'AOM_0004','2011-10-3 9:30:00'
insert into tb select 'AOM_0005','2011-10-3 15:25:00'
insert into tb select 'AOM_0006','2011-10-3 16:20:00'
insert into tb select 'AOM_0007','2011-10-5 10:20:00'
insert into tb select 'AOM_0008','2011-10-6 11:20:00'
insert into tb select 'AOM_0009','2011-10-6 12:20:00'
go
select convert(varchar(10),起单时间,120)日期,count(*)起单件数
from tb
group by convert(varchar(10),起单时间,120)
/*
日期         起单件数
---------- -----------
2011-10-01 2
2011-10-02 1
2011-10-03 3
2011-10-05 1
2011-10-06 2

(5 行受影响)

*/
go
drop table tests

[--小F--]

select
  convert(varchar(10),起单时间,120) as 日期,
  count(1) as 起单件数
from
  tb
group by
  convert(varchar(10),起单时间,120)

[zlp321002]

select CONVERT(varchar(10),getdate(),120)日期,COUNT(1) 起单件数
from tb
group by CONVERT(varchar(10),getdate(),120),

[zlp321002]

select CONVERT(varchar(10),起单时间,120)日期,COUNT(1) 起单件数
from tb
group by CONVERT(varchar(10),getdate(),120),

[--小F--]

----------------------------------------------------------------
-- Author  :fredrickhu(小F，向高手学习)
-- Date    :2011-10-25 13:18:42
-- Version:
--      Microsoft SQL Server 2008 R2 (RTM) - 10.50.1617.0 (Intel X86) 
--	Apr 22 2011 11:57:00 
--	Copyright (c) Microsoft Corporation
--	Enterprise Evaluation Edition on Windows NT 6.1 <X64> (Build 7600: ) (WOW64)
--
----------------------------------------------------------------
--> 测试数据：[tb]
if object_id('[tb]') is not null drop table [tb]
go 
create table [tb]([表单号] varchar(8),[起单时间] datetime)
insert [tb]
select 'AOM_0001','2011-10-1 10:20:00' union all
select 'AOM_0002','2011-10-1 12:30:00' union all
select 'AOM_0003','2011-10-2 13:20:00' union all
select 'AOM_0004','2011-10-3 9:30:00' union all
select 'AOM_0005','2011-10-3 15:25:00' union all
select 'AOM_0006','2011-10-3 16:20:00' union all
select 'AOM_0007','2011-10-5 10:20:00' union all
select 'AOM_0008','2011-10-6 11:20:00' union all
select 'AOM_0009','2011-10-6 12:20:00'
--------------开始查询--------------------------
select distinct convert(varchar(10),起单时间,120) as 日期, COUNT(1) over(partition by  convert(varchar(10),起单时间,120)) from tb
----------------结果----------------------------
/* 日期         
---------- -----------
2011-10-01 2
2011-10-02 1
2011-10-03 3
2011-10-05 1
2011-10-06 2

(5 行受影响)

*/

[BTbug]

谢谢各位！！！已经解决问题。