SQL查询一批数据，怎么在最后一行增加个合计

示例代码：
select
case when yf is not null then yf else '合计' end yf,
sum(cast(bqbj1 as money)) bjhz,
sum(cast(bqll1 as money)) lxhz,
sum(cast(bqwh as money)) whhz
from (select SUBSTRING(rq,6,2) yf,bqbj1,bqll1,bqwh
from formtable_main_84_dt1 d
where rq between '2017-07-01' and '2017-09-30') as a
group by yf
with rollup