求SQL语句

Question

数据模式如下:  cm_id         cm_company             create_date        cm_name
-------------------------------------------------------------------------
    1              aaaa             2009-2-3 9:13:12        a
    2              bbbb             2009-2-4 9:13:12        b
    3              aaaa             2009-2-5 9:13:12        c
    4              aaaa             2009-2-6 9:13:12        d
    5              cccc             2009-2-7 9:13:12        e
 
查找的数据要符合以下要求:
如果cm_company字段的内容相同，只调用注册时间最早的那个数据,查询得到的数据如下：  cm_id         cm_company             create_date        cm_name
-------------------------------------------------------------------------
    1              aaaa             2009-2-3 9:13:12        a
    2              bbbb             2009-2-4 9:13:12        b
    5              cccc             2009-2-7 9:13:12        e
 求一SQL语句，谢谢大牛们啦

Answer 1

select *
from ta a
where not exists(select 1 from ta where cm_company = a.cm_company and create_date < a.create_date)

Answer 2

--抢SF不建表
SELECT * FROM T T1
WHERE NOT EXISTS(
SELECT DISTINCT 1 FROM T T2 WHERE T2.CM_COMPANY=T1.CM_COMPANY AND T2.CREATE_DATE<T1.CREATE_DATE
)

Answer 3

----------------------------------------------------------------
-- Author :fredrickhu(小F 向高手学习)
-- Date   :2009-07-27 17:21:55
----------------------------------------------------------------
--> 测试数据：[tb]
if object_id('[tb]') is not null drop table [tb]
create table [tb]([cm_id] int,[cm_company] varchar(4),[create_date] datetime,[cm_name] varchar(1))
insert [tb]
select 1,'aaaa','2009-2-3 9:13:12','a' union all
select 2,'bbbb','2009-2-4 9:13:12','b' union all
select 3,'aaaa','2009-2-5 9:13:12','c' union all
select 4,'aaaa','2009-2-6 9:13:12','d' union all
select 5,'cccc','2009-2-7 9:13:12','e'
--------------开始查询--------------------------select
     * 
from 
    [tb] t
where 
   not exists
(select 1 from tb where cm_company=t.cm_company and cm_id<t.[cm_id])
----------------结果----------------------------
/*cm_id       cm_company create_date                                            cm_name 
----------- ---------- ------------------------------------------------------ ------- 
1           aaaa       2009-02-03 09:13:12.000                                a
2           bbbb       2009-02-04 09:13:12.000                                b
5           cccc       2009-02-07 09:13:12.000                                e（所影响的行数为 3 行）
*/