SQL - How to remove from the total what has already been counted - sql

Question

I'm asking ur help
here this is my set
ID date_answered
---------- --------------
1 16/09/19
2 16/09/19
3 16/09/19
4 16/09/19
5 16/09/19
6 16/09/19
7 16/09/19
8 16/09/19
9 16/09/19
10 17/09/19
11 17/09/19
12 17/09/19
13 18/09/19
14 18/09/19
15 18/09/19
16 18/09/19
17 19/09/19
18 19/09/19
19 19/09/19
20 19/09/19
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
as you can see :
16/09/2019 there are 9 people who answered
17/09/2019 there are 7 people who answered
18/09/2019 there are 4 people who answered
19/09/2019 there are 4 people who answered
there are still 20 people who didnt answer
to calculate how many people answered per day, i have done :
nb_answered = count(id) over (partition by date_answered order by date_answered)
now my problem is there, i'm trying to get that :
date_answered nb_answered nb_left
--------------- -------------- --------
16/09/2019 9 40
17/09/2019 7 31(40-9)
18/09/2019 4 24(31-7)
19/09/2019 4 20(24-4)
i have tried :
count(id) over (order by date_complete rows between UNBOUNDED PRECEDING AND UNBOUNDED FOLLOWING) which give me 40 (total person).
it's cool for the first date, but when i move to the second date i dont know how to have 31.
How can I do that: every day I remove from the total, the number that has already answered
Do you have any suggestion ?

Answer 1

Another option might be correlated subquery in SELECT statement.
Example is a little bit simplified (didn't feel like typing that much).
SQL> with test (id, da) as
2 (select 1, 16092019 from dual union all
3 select 2, 16092019 from dual union all
4 select 3, 16092019 from dual union all
5 select 4, 16092019 from dual union all
6 select 5, 16092019 from dual union all
7 --
8 select 6, 17092019 from dual union all
9 select 7, 17092019 from dual union all
10 select 8, 17092019 from dual union all
11 --
12 select 9, 19092019 from dual union all
13 --
14 select 10, null from dual union all
15 select 11, null from dual union all
16 select 12, null from dual union all
17 select 13, null from dual
18 )
19 select a.da date_answered,
20 count(a.id) nb_answered,
21 (select count(*) from test b
22 where b.da >= a.da
23 or b.da is null
24 ) nb_left
25 from test a
26 group by a.da
27 order by a.da;
DATE_ANSWERED NB_ANSWERED NB_LEFT
------------- ----------- ----------
16092019 5 13
17092019 3 8
19092019 1 5
4 4
SQL>

Answer 2

You want to subtract the overall count from the cumulative count:
select date_answered, count(*) as answered_on_date,
( count(*) over () -
sum(count(*)) over (order by date_answered nulls last)
) as remaining
from t
group by date_answered
order by date_answered;
If you don't want to include the current date, then subtract that as well:
select date_answered, count(*) as answered_on_date,
( count(*) over () -
sum(count(*)) over (order by date_answered nulls last) -
count(*)
) as remaining
from t
group by date_answered
order by date_answered;