WITH I AS 
(
	SELECT ID, Val FROM 
	(
		SELECT 1 AS ID,'item1' AS Val UNION ALL
		SELECT 2 AS ID,'item1' AS Val UNION ALL
		SELECT 3 AS ID,'item2' AS Val UNION ALL
		SELECT 4 AS ID,'item2' AS Val UNION ALL
		SELECT 5 AS ID,'item2' AS Val UNION ALL
		SELECT 6 AS ID,'item2' AS Val UNION ALL
		SELECT 7 AS ID,'item1' AS Val UNION ALL
		SELECT 8 AS ID,'item3' AS Val UNION ALL
		SELECT 9 AS ID,'item3' AS Val 
	) A
),
I2 AS
(
	SELECT 
		Id,
		Val,
		RN1 = ROW_NUMBER() OVER (PARTITION BY Val Order BY ID),
		RN2 = ROW_NUMBER() OVER (Order BY ID)
	FROM I
)
SELECT Val, COUNT(*) FROM I2
GROUP BY Val, RN2 - RN1
ORDER BY MIN(ID)