Sum over N days excluding Weekends and Holidays - sql

Question

I have below table
AccountID
Date
Amount
123
07/02/2021
2000
123
07/09/2021
9000
123
07/15/2021
500
123
07/20/2021
500
123
07/28/2021
500
I am trying to create a test script to test data for just one month(July). I want to sum the amount over 5 days where 5 days does not count weekends and holidays. Since it is month of July the holiday falls on July 5th 2021(07/05/2021).
The output should look something like below
AccountID
Date
Amount
123
07/02/2021
11000
123
07/09/2021
9500
123
07/15/2021
1000
123
07/20/2021
500
123
07/28/2021
500
Below is the table create and data insert statements for reference :-
create table TRANSACTIONS (
AccountID int,
Date date,
Amount int
)
insert into TRANSACTIONS values (123, '07/02/2021', 2000)
insert into TRANSACTIONS values (123, '07/09/2021', 9000)
insert into TRANSACTIONS values (123, '07/15/2021', 500)
insert into TRANSACTIONS values (123, '07/20/2021', 500)
insert into TRANSACTIONS values (123, '07/28/2021', 500)
I was able to create script that could sum over 5 days with skipping weekends(Saturday and Sunday). I am not able to think how can I skip the holiday on July 5th, 2021. I am fine with hardcoding it since this is just for testing purposes. The code 'DATEPART(WEEKDAY, h2.Date) not in (1, 7)' skips Weekend and 'DATEADD(d, 6, h1.Date)' here I am adding 6 and not 5 even the sum should be for over 5 days because after reading some articles I figured that in skipping weekends the last day is not inclusive so used 6 instead of 5. This code adds perfectly over 5 days skipping weekends
SELECT AccountId, Date,
(
SELECT SUM(Amount)
FROM TRANSACTIONS h2
WHERE
h1.AccountID = h2.AccountID and
DATEPART(WEEKDAY, h2.Date) not in (1, 7) and
h2.Date between h1.Date AND DATEADD(d, 6, h1.Date)
) as SumAmount
FROM TRANSACTIONS h1

Answer 1

The only sane way to tackle this is to have a calendar table to represent holidays. The easiest approach is to store every date for the date range you're likely to need (eg 1970-2030) with the type of the date, perhaps and enum of WORKDAY, WEEKEND, HOLIDAY or whatever works, eg
CREATE TABLE CALENDAR (
Date DATE,
Day_type varchar(16)
);
-- insert rows for dates you care about
Depending on where you live, you may need to include a region column too (typically the country and/or state).
With such a table, you join to it:
SELECT
AccountId,
DATEADD(DAY, (DATEDIFF(DAY, 0, t.Date)/7)*7 + 7, 0) as Date,
SUM(Amount)
FROM TRANSACTIONS t
JOIN CALENDAR c on t.Date = c.Date
AND c.day_type = 'WORKDAY'
WHERE t.Date BETWEEN <your date range>
GROUP BY AccountId, DATEADD(DAY, (DATEDIFF(DAY, 0, t.Date)/7)*7 + 7, 0)