我认为计算是：
select t.*,
premium / (12 / yearly_payment_freq)) as monthly_premium_calculated
from mytable t;
编辑：
我知道，您还需要在中间几个月内进行这种分配。因此，您可以通过计算非零付款的数量来分配组。然后：
select t.*,
( max(premium) over (partition by policy_id, grp) /
(12 / yearly_payment_freq)
) as monthly_premium_calculated
from (select t.*,
sum(case when premium > 0 then 1 else 0 end) over (partition by policy_id order by payment_date) as grp
from mytable t
) t;
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