Alternate approach for getting Minimum of Column B that falls under Max of Column A

declare @a table(col1 datetime, col2 datetime)
insert into @a select
'20120520', '20120620' union all select
'20120520', '20120513' union all select
'20120530', '20120620' union all select
'20120530', '20120515' union all select
'20120630', '20120515' union all select
'20120630', '20120510' union all select
'20120630', '20120525' 
--First approach
SELECT	*
FROM	(
		SELECT	*, RN = ROW_NUMBER() OVER (ORDER BY col1 DESC, col2)
		FROM	@a
		)a
WHERE	RN = 1;

--Second Approach
select	col1, Col2 = min(Col2)
from	@a t
where	t.col1 = (select max(col1) from @a)
group by col1

/* OUTPUT 
col1	                Col2
2012-06-30 00:00:00.000	2012-05-10 00:00:00.000
*/