How to select maximum per column-value in SQL?

In SQL Server, I have a list of integers, datetimes, and st开发者_如何学JAVArings. For example,

number  datetime             string
6       2011-09-22 12:34:56  nameOne
6       2011-09-22 1:23:45   nameOne
6       2011-09-22 2:34:56   nameOne
5       2011-09-22 3:45:01   nameOne
5       2011-09-22 4:56:01   nameOne
5       2011-09-22 5:01:23   nameOne
7       2011-09-21 12:34:56  nameTwo
7       2011-09-21 1:23:45   nameTwo
7       2011-09-21 2:34:56   nameTwo
4       2011-09-21 3:45:01   nameTwo
4       2011-09-21 4:56:01   nameTwo
4       2011-09-21 5:01:23   nameTwo

I would to write a SQL statement that outputs only those rows whose number is a maximum for each string. In this example,

number  datetime             string
6       2011-09-22 12:34:56  nameOne
6       2011-09-22 1:23:45   nameOne
6       2011-09-22 2:34:56   nameOne
7       2011-09-21 12:34:56  nameTwo
7       2011-09-21 1:23:45   nameTwo
7       2011-09-21 2:34:56   nameTwo

I know that I could loop over each string in the string column, then get the maximum for that string, then select the rows matching that maximum. For example,

declare @max int
declare my_cursor cursor fast_forward for
    select distinct string
    from table
open my_cursor
fetch next from my_cursor into @string
while @@fetch_status = 0
begin
    set @max = (select max(number) from table where string = @string)
    select * from table where number = @max
    fetch next from my_cursor into @string
end
close my_cursor
deallocate my_cursor

However, I am wondering if there is a way to accomplish this task WITHOUT using a loop (e.g., by using aggregate functions and grouping).

---

;WITH T as
(
SELECT *,
       RANK() OVER (PARTITION BY string ORDER BY number DESC) RN
FROM YourTable
)
SELECT number,
       datetime,
       string
FROM T
WHERE RN=1;

---

WITH maxes AS (
    SELECT string, MAX(number) AS max_number
    FROM tbl
    GROUP BY string
)
SELECT tbl.*
FROM tbl
INNER JOIN maxes
    ON maxes.string = tbl.string AND maxes.max_number = tbl.number