How do I sum until it meets a criteria?

I have the following data set for an user. I want to merge the False flag rows to the latest True row.

initial set:

user    input_date  starting_balance deposit flag
user1   2020-08-20         100           20   TRUE
user1   2020-08-21         200            0   TRUE
user1   2020-08-23         null         200   FALSE
user1   2020-08-24         300          130   TRUE
user1   2020-08-25         400          0     TRUE

output:

user    input_date  starting_balance deposit flag
user1   2020-08-20         100           20   TRUE
user1   2020-08-21         200            0   TRUE
user1   2020-08-24         300          330   TRUE
user1   2020-08-25         400          0     TRUE

sql to recreate data:

select 'user1' as user, '2020-08-20' as input_date, 100 as starting_balance, 20 as deposit, true as flag
union all
select 'user1', '2020-08-21', 200, 0, true
union all
select 'user1', '2020-08-23', null, 200, false
union all
select 'user1', '2020-08-24', 300, 130, true
union all
select 'user1', '2020-08-25', 400, 0, true;

Answer

This is an aggregation problem. You can use a cumulative sum to assign groups. And then aggregate. The group is the number of “trues” up to each row. So:

select user, max(input_date), sum(starting_balance),
       sum(deposit), true as flag
from (select t.*,
             sum(case when flag then 1 else 0 end) over (partition by user order by input_date desc) as grp
      from t
     ) t
group by user, grp
order by user, input_date;