SQL列最大重复项

 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