declare @a table(col1 varchar(10), col2 varchar)
insert into @a select 
'a', 1 union all select
'a', 5 union all select
'a', 7 union all select
'b', 1 union all select
'b', 3 union all select
'c', 1


;WITH Cte AS
(
	SELECT col1, col2, ROW_NUMBER() OVER (PARTITION BY col1 ORDER BY col2 ASC) AS RowNum
	FROM @a
)


SELECT 
	A.Col1,
	COALESCE(B.Col2, A.Col2) AS col2
FROM
	Cte AS A
LEFT OUTER JOIN
	Cte AS B
	ON A.col1 = B.col1
	AND A.RowNum + 1 = B.RowNum
WHERE
	A.RowNum = 1
	OR B.RowNum = 2

query 1
-------
SELECT	*
FROM	@a a
OUTER APPLY(
	SELECT TOP 1 *
	FROM	(SELECT TOP 2 *
		FROM	@a b
		WHERE	a.col1 = b.col1
		ORDER BY col2)tmp
	ORDER BY col2 DESC)tmp

query 2
-------
SELECT	*
FROM	@a a
OUTER APPLY(
	SELECT	*
	,	rn = ROW_NUMBER() OVER (PARTITION BY col1 ORDER BY col2)
	,	cnt = COUNT(1) OVER (PARTITION BY col1)
	FROM	@a b
	WHERE	a.col1 = b.col1
	)tmp
WHERE	(cnt = 3 AND rn = cnt - 1) 
	OR (cnt = 2 AND rn = cnt)
	OR (cnt = 1 AND rn = 1)