SELECT	t2.Month , t2.Category1, t2.Segment, t2.Scheme, GMV, ParentID,
	count() over (partition by ParentID order by Month asc) as Churn 
	FROM 
		(
			select toYYYYMM(Date) Month, ParentID, GMV, Category1, SupplierSegment as Segment, Scheme
			from DP_GMV_Forecast.test
			where GMV=0 and ParentID=1228517030000 --and Category1='Miscellaneous accessories' and Scheme='FBS'
			group by toYYYYMM(Date), ParentID,Category1, SupplierSegment, Scheme, GMV
		) t2
	group by t2.Month , t2.Category1, t2.Segment, t2.Scheme, GMV, ParentID  settings  allow_experimental_window_functions = 1;