How to count only the working days between two dates? - sql

Question

I have the following table called vacations, where the employee number is displayed along with the start and end date of their vacations:
id_employe
start
end
1001
2020-12-24
2021-01-04
What I am looking for is to visualize the amount of vacation days that each employee had, but separating them by employee number, month, year and number of days; without taking into account non-business days (Saturdays, Sundays and holidays).
I have the following query, which manages to omit Saturday and Sunday from the posting:
SELECT id_employee,
EXTRACT(YEAR FROM t.Date) AS year,
EXTRACT(MONTH FROM t.Date) AS month,
SUM(WEEKDAY(`Date`) < 5) AS days
FROM (SELECT v.id_employee,
DATE_ADD(v.start, interval s.seq - 1 DAY) AS Date
FROM vacations v CROSS JOIN seq_1_to_100 s
WHERE DATE_ADD(v.start, interval s.seq - 1 DAY) <= v.end
ORDER BY v.id_employee, v.start, s.seq ) t
GROUP BY id_employee, EXTRACT(YEAR_MONTH FROM t.Date);
My question is, how could I in addition to skipping the weekends, also skip the holidays? I suppose that I should establish another table where the dates of those holidays are stored, but how could my * query * be adapted to perform the comparison?
If we consider that the employee 1001 took his vacations from 2020-12-24 to 2021-01-04 and we take Christmas and New Years as holidays, we should get the following result:
id_employee
month
year
days
1001
12
2020
5
1001
1
2021
1

Answer 1

After you have created a table that stores the holiday dates, then you probably can do something like this:
SELECT id_employee,
EXTRACT(YEAR FROM t.Date) AS year,
EXTRACT(MONTH FROM t.Date) AS month,
SUM(CASE WHEN h.holiday_date IS NULL THEN WEEKDAY(`Date`) < 5 END) AS days
FROM (SELECT v.id_employee,
DATE_ADD(v.start, interval s.seq - 1 DAY) AS Date
FROM vacations v CROSS JOIN seq_1_to_100 s
WHERE DATE_ADD(v.start, interval s.seq - 1 DAY) <= v.end
ORDER BY v.id_employee, v.start, s.seq ) t
LEFT JOIN holidays h ON t.date=h.holiday_date
GROUP BY id_employee, EXTRACT(YEAR_MONTH FROM t.Date);
Assuming that the holidays table structure would be something like this:
CREATE TABLE holidays (
id INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
holiday_date DATE,
holiday_description VARCHAR(255));
Then LEFT JOIN it to your current query and change the SUM() slightly by adding CASE expression to check. If the ON t.date=h.holiday_date in the left join matches, there will be result of field h.holiday_date, otherwise it will be NULL, hence only the CASE h.holiday_date WHEN IS NULL .. will be considered.
Demo fiddle
Adding this solution compatible with both MariaDB and MySQL version that supports common table expression:
WITH RECURSIVE cte AS
(SELECT id_employee, start, start lvdt, end FROM vacations
UNION ALL
SELECT id_employee, start, lvdt+INTERVAL 1 DAY, end FROM cte
WHERE lvdt+INTERVAL 1 DAY <=end)
SELECT id_employee,
YEAR(v.lvdt) AS year,
MONTH(v.lvdt) AS month,
SUM(CASE WHEN h.holiday_date IS NULL THEN WEEKDAY(v.lvdt) < 5 END) AS days
FROM cte v
LEFT JOIN holidays h
ON v.lvdt=h.holiday_date
GROUP BY id_employee,
YEAR(v.lvdt),
MONTH(v.lvdt);