As per my requirement , it would be something :

SELECT

CId,

CCId,

CCount,

(select 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)

from SampleData

but it's giving error.