Get day by day repeated data with postgres - sql

Question

I have transactions table with columns id, user_id, currency, amount and created_at;
I want to write function to check in last x days transaction with exist amount repeated or not.
For example user makes transaction per 200$ in 5 days, and 6th days wants to make transaction in 250$. Function have to check did user make transaction in last 5 days per 250$ or not. In this example function have to return false. Because user breaks rule.
If user want to make transaction with 200$ function have to return true;
I have tried with
select count(*) from "transactions" where "created_at" >= NOW()- INTERVAL '5 DAY' and "amount"=250 and "currency" = "USD"
but this gives me incorrect answer, becouse if user makes a transaction twise a day, this function calculates 5 items in 4 day. If n transactions in a day I have to calculate it 1 transaction.
So:
id user_id currency amount created_at
1 1 USD 200 2021-05-15 16:00:01
2 1 USD 200 2021-05-16 18:05:28
3 1 USD 200 2021-05-17 11:33:55
4 1 USD 200 2021-05-18 12:00:01
5 1 USD 200 2021-05-18 13:15:01
6 2 USD 250 2021-05-15 16:00:01
7 2 USD 250 2021-05-16 18:05:28
8 2 USD 250 2021-05-17 11:33:55
9 2 USD 250 2021-05-18 12:00:01
10 2 USD 250 2021-05-19 13:15:01
with this data, query have to return 4 items for user with id 1 and amount 200. Have to return 5 items for user with id 2 and amount 250

Answer 1

I think you just want count(distinct). You seem to want different values for each user, so that suggests group by as well:
select user_id, count(distinct created_at::date) as num_days
from "transactions"
where created_at >= NOW()- INTERVAL '5 DAY' and
amount = 250 and
currency = 'USD'
group by user_id;