按照某个字段分组，取出最大的一条记录

请教一个sql（按某个字段分组然后从每组取出最大的一条纪录）？

请教一个sql（按某个字段分组然后从每组取出最大的一条纪录）？

比如表 data_table

字段有：id、name、address、tel、update

1 n1 a1 s1 20070801

2 n2 a1 s2 20070302

3 n3 a2 s3 20070501

4 n3 a2 s3 20070301

我想得到的数据是 按照 address 分组 然后取出每组中update最大的那几条纪录。结果应该是这两条纪录：

1 n1 a1 s1 20070801

3 n3 a2 s3 20070501

请问怎么写sql？谢谢

------解决方案--------------------------------------------------------

select id, name, address, tel, update

from (

select id, name, address, tel, update,

row_number() over(partition by address order by update desc) rn

from data_table

)

where rn = 1

------解决方案--------------------------------------------------------

SELECT * FROM A,(SELECT A.address,MAX(A.update) FROM A GROUP BY A.address) C

WHERE A.address = C.address

AND A.update = C.update

------解决方案--------------------------------------------------------

SQL> select *

2 from (

3 select tt.*,

4 row_number() over(partition by tt.address order by tt.update1 desc) rn

5 from (

6 select 1 as id, 'n1 ' as name, 'a1 ' as address, 's1 ' as tel, '20070801 ' as update1 from dual

7 union all

8 select 2 as id, 'n2 ' as name, 'a1 ' as address, 's2 ' as tel, '20070302 ' as update1 from dual

9 union all

10 select 3 as id, 'n3 ' as name, 'a2 ' as address, 's3 ' as tel, '20070501 ' as update1 from dual

11 union all

12 select 4 as id, 'n3 ' as name, 'a2 ' as address, 's3 ' as tel, '20070301 ' as update1 from dual

13 )tt

14 )zz

15 where zz.rn = 1;

ID NAME ADDRESS TEL UPDATE1 RN

---------- ---- ------- --- -------- ----------

1 n1 a1 s1 20070801 1

3 n3 a2 s3 20070501 1

------解决方案--------------------------------------------------------

select *

from data_table t

where not exists(select 1

from data_table

where address=t.address

and update> t.update)