Пытаюсь через dateadd и @ReportDate сделать ограничение по месяцу вместо использования appl_month. Подскажите как правильно это сделать.

Примерный запрос:

DECLARE @ReportDate date
SET @ReportDate = '01.09.2020'
select appl_month
, (sum(case when financed = 1 and appl_month = '2020-07' then app_PS_2mob end)
/ sum(case when financed = 1 and appl_month = '2020-07' then cash_to_client end))
/ cast((sum(case when financed = 1 and appl_month = '2020-07' then app_PS_1mob end)
/ sum(case when financed = 1 and appl_month = '2020-07' then cash_to_client end)) as float) as Рои2наРои1_07

, (sum(case when financed = 1 and appl_month = '2020-06' then app_PS_2mob end)
/ sum(case when financed = 1 and appl_month = '2020-06' then cash_to_client end))
/ cast((sum(case when financed = 1 and appl_month = '2020-06' then app_PS_1mob end)
/ sum(case when financed = 1 and appl_month = '2020-06' then cash_to_client end)) as float) as Рои2наРои1_06

from DWH
where date_time >= '01-01-2020'
and date_time <='12-31-2020'
group by appl_month
order by appl_month