Is it possible to add a identity to a GROUP BY using SQL?

Question

Is it possible to add a identity column to a GROUP BY so that each duplicate has a identity number?

My original data looks like this:

1    AAA  [timestamp]
2    AAA  [timestamp]
3    BBB  [timestamp]
4    CCC  [timestamp]
5    CCC  [timestamp]
6    CCC  [timestamp]
7    DDD  [timestamp]
8    DDD  [timestamp]
9    EEE  [timestamp]
....

And I want to convert it to:

1    AAA   1
2    AAA   2
4    CCC   1
5    CCC   2
6    CCC   3
7    DDD   1
8    DDD   2
...

The solution was:

CREATE PROCEDURE [dbo].[RankIt]
AS
BEGIN
SET NOCOUNT ON;

SELECT  *, RANK() OVER(PARTITION BY col2 ORDER BY timestamp DESC) AS ranking 
FROM MYTABLE;

END

Answer 1

You could try using ROW_NUMBER if you are using Sql Server 2005

DECLARE @Table TABLE(
        ID INT,
        Val VARCHAR(10)
)

INSERT INTO @Table SELECT 1,'AAA'
INSERT INTO @Table SELECT 2,'AAA'
INSERT INTO @Table SELECT 3,'BBB' 
INSERT INTO @Table SELECT 4,'CCC' 
INSERT INTO @Table SELECT 5,'CCC' 
INSERT INTO @Table SELECT 6,'CCC' 
INSERT INTO @Table SELECT 7,'DDD' 
INSERT INTO @Table SELECT 8,'DDD' 
INSERT INTO @Table SELECT 9,'EEE' 

SELECT  *,
        ROW_NUMBER() OVER(PARTITION BY VAL ORDER BY Val)
FROM    @Table

Answer 2

create table #testalot
(
  [id] int identity,
  data varchar(50)
)

insert #testalot (data) values('AAA')
insert #testalot (data) values('AAA')
insert #testalot (data) values('BBB')
insert #testalot (data) values('CCC')
insert #testalot (data) values('CCC')
insert #testalot (data) values('CCC')
insert #testalot (data) values('DDD')
insert #testalot (data) values('DDD')

select *,ROW_NUMBER() OVER(PARTITION BY data ORDER BY data DESC) AS 'Number'
 from #testalot

 drop table #testalot

returns

id  data Number
1   AAA  1
2   AAA  2
3   BBB  1
4   CCC  1
5   CCC  2
6   CCC  3
7   DDD  1
8   DDD  2