--測試數據
DECLARE @t TABLE(ID int PRIMARY KEY,col decimal(10,2))
INSERT @t SELECT 1 ,26.21
UNION ALL SELECT 2 ,88.19
UNION ALL SELECT 3 , 4.21
UNION ALL SELECT 4 ,76.58
UNION ALL SELECT 5 ,58.06
UNION ALL SELECT 6 ,53.01
UNION ALL SELECT 7 ,18.55
UNION ALL SELECT 8 ,84.90
UNION ALL SELECT 9 ,95.60

--統計
SELECT a.Description,
	Record_count=COUNT(b.ID),
	[Percent]=CASE 
		WHEN Counts=0 THEN '0.00%'
		ELSE CAST(CAST(
			COUNT(b.ID)*100./c.Counts
			as decimal(10,2)) as varchar)+'%'
		END
FROM(
	SELECT sid=1,a=NULL,b=30  ,Description='<30' UNION ALL
	SELECT sid=2,a=30  ,b=60  ,Description='>=30 and <60' UNION ALL
	SELECT sid=3,a=60  ,b=75  ,Description='>=60 and <75' UNION ALL
	SELECT sid=4,a=75  ,b=95  ,Description='>=75 and <95' UNION ALL
	SELECT sid=5,a=95  ,b=NULL,Description='>=95' 
)a LEFT JOIN @t b 
	ON (b.col<a.b OR a.b IS NULL)
		AND(b.col>=a.a OR a.a IS NULL)
	CROSS JOIN(
		SELECT COUNTS=COUNT(*) FROM @t
	)c
GROUP BY a.Description,a.sid,c.COUNTS
ORDER BY a.sid
/*--結果:
Description    Record_count  Percent
------------------- ------------------ ---------------------- 
<30          3            33.33%
>=30 and <60  2            22.22%
>=60 and <75  0            0.00%
>=75 and <95  3            33.33%
>=95         1            11.11%
--*/