;WITH SampleData AS (

SELECT CId = 1, CCId = 'a', CCount = 3, totalCount = 6 UNION ALL

SELECT 1, 'a', 3, 6 UNION ALL

SELECT 1, 'b', 3, 6 UNION ALL

SELECT 1, 'c', 3, 6 UNION ALL

SELECT 2, 'b', 2, 6 UNION ALL

SELECT 2, 'b', 2, 6 UNION ALL

SELECT 2, 'a', 2, 6 UNION ALL

SELECT 2, 'a', 2, 6 UNION ALL

SELECT 3, 'v', 1, 6

)

SELECT

CId,

CCId,

CCount,

totalCount = SUM([First]) OVER (PARTITION BY (SELECT NULL))

FROM (

SELECT *,

[First] = CASE WHEN 1 = ROW_NUMBER() OVER(PARTITION BY CId ORDER BY CCId) THEN CCount END

FROM SampleData

) d