;with cte as (
	select
		[buffer]=case when [plan]>=1 then 0 else [plan] end
		,plan_smalli=case when [plan]>=1 then floor([plan]) end
		, ... 
	from T 
	where rn=1
	
	union all
	
	select
		[buffer]=case when cte.[buffer]+T.[plan]>=1 then 0 else cte.[buffer]+T.[plan] end
		,plan_smalli=case when cte.[buffer]+T.[plan]>=1 then floor(cte.[buffer]+T.[plan]) end
		, ...
	from cte inner join T on cte.rn=T.rn-1)
select * from cte order by rn 

with a as
    (select * from(values(201908,0.298645),(201907,0.395862),(201906,0.496441),(201905,0.594498),(201904,0.613721),(201903,0.72629)
                        ,(201902,0.819897),(201901,1.184565))a(a,b))
select *,case when floor(c)>floor(c-b) then floor(c)-floor(c-b) end d
  from (select *,sum(b)over(order by a desc rows between unbounded preceding and current row) c
          from a)b