SELECT t.Col1,
t.Col2
FROM
(
SELECT ROW_NUMBER() OVER(PARTITION BY Col1 ORDER BY Col2 DESC) AS RowNo,
Col1,
Col2
FROM Table
)t
WHERE t.RowNo=1

--Generate some randomish data
--500,000 Rows
Drop Table #tmp
Create Table #tmp (col1 int, col2 int)
Declare @cnt int
Set @cnt = 0

While @cnt < 100000 Begin
	Insert Into #tmp Select @cnt, @cnt % 5 * 10
	Insert Into #tmp Select @cnt, @cnt % 6 * 20
	Insert Into #tmp Select @cnt, @cnt % 7 * 30
	Insert Into #tmp Select @cnt, @cnt % 8 * 40
	Insert Into #tmp Select @cnt, @cnt % 9 * 50
	Set @cnt = @cnt + 1
End

--Peso
SELECT Col1, Max(Col2) FROM #tmp 
GROUP BY Col1 ORDER BY Col1
/*
SQL Server parse and compile time: 
   CPU time = 0 ms, elapsed time = 23 ms.

(100000 row(s) affected)
Table '#tmp'. Scan count 3, logical reads 1104, physical reads 0, 
	read-ahead reads 0, lob logical reads 0, lob physical reads 0, 
	lob read-ahead reads 0.
Table 'Worktable'. Scan count 0, logical reads 0, physical reads 0, 
	read-ahead reads 0, lob logical reads 0, lob physical reads 0, 
	lob read-ahead reads 0.

SQL Server Execution Times:
   CPU time = 719 ms,  elapsed time = 1416 ms.
*/

--visakh16
SELECT t.Col1,t.Col2
FROM
(
	SELECT 
	ROW_NUMBER() 
		OVER(PARTITION BY Col1 
		ORDER BY Col2 DESC) AS RowNo,
	Col1, Col2
	FROM #tmp
) t
WHERE t.RowNo = 1
ORDER BY Col1
/*
SQL Server parse and compile time: 
   CPU time = 0 ms, elapsed time = 21 ms.

(100000 row(s) affected)
Table '#tmp'. Scan count 3, logical reads 1104, physical reads 0, 
	read-ahead reads 0, lob logical reads 0, lob physical reads 0, 
	lob read-ahead reads 0.

SQL Server Execution Times:
   CPU time = 1545 ms,  elapsed time = 2387 ms.
*/