SELECT 1 AS co1, 'a' AS co2

INTO #a

UNION

SELECT  2, 'a'

UNION

SELECT  11,'a'

UNION

SELECT 12, 'a'

UNION

SELECT 13, 'a'

UNION

SELECT 14, 'a'

UNION

SELECT 15, 'a'

UNION

SELECT 3, 'b'

UNION

SELECT 7, 'b'

UNION

SELECT 8, 'b'

UNION

SELECT  9, 'b'

UNION

SELECT  10, 'b'

UNION

SELECT 4, 'c'

UNION

SELECT 5, 'c'

UNION

SELECT 6, 'c'

SELECT * FROM #a

  --第二步：操作

  SELECT co2,MAX(counts) counts FROM

(

 SELECT rowid,co2,SUM(co1) counts FROM

 (

  SELECT co1*-1 co1,co2,ROW_NUMBER() OVER (ORDER BY co1) rowid  FROM #a a

  WHERE NOT EXISTS (SELECT * FROM #a WHERE co1=a.co1-1 AND co2=a.co2)

  UNION ALL

  SELECT co1+1,co2,ROW_NUMBER() OVER (ORDER BY co1) rowid FROM #a a

  WHERE NOT EXISTS (SELECT * FROM #a WHERE co1=a.co1+1 AND co2=a.co2)

  ) p

 GROUP BY rowid,co2

) p1

GROUP BY co2

DROP TABLE #a