How to count days between 2 dates except holiday and weekend? - mysql

Question

I started a HR management project and I want to count days between 2 dates without counting the holidays and weekends. So the HR can count employee's day off
Here's the case, I want to count between 2018-02-14 and 2018-02-20 where there is an office holiday on 2018-02-16. The result should be 3 days.
I have already created a table called tbl_holiday where I put all weekends and holidays in one year there
I found this post, and I tried it on my MariaDB
Here's my query:
SELECT 5 * (DATEDIFF('2018-02-20', '2018-02-14') DIV 7) +
MID('0123444401233334012222340111123400012345001234550', 7 *
WEEKDAY('2018-02-14') + WEEKDAY('2018-02-20') + 1, 1) -
(SELECT COUNT(dates) FROM tbl_holiday WHERE dates NOT IN (SELECT dates FROM tbl_holiday)) as Days
The query works but the result is 4 days, not 3 days. It means the query only exclude the weekends but not the holiday
What is wrong with my query? Am I missing something? Thank you for helping me

Answer 1

#RichardDoe, from the question comments.
In a reasonable implementation of a date table, you create a list of all days (covering a sufficient range to cope with any query you may run against it - 15 years each way from today is probably a useful minimum), and alongside each day you store a variety of derived attributes.
I wrote a Q&A recently with basic tools that would get you started in SQL Server: https://stackoverflow.com/a/48611348/9129668
Unfortunately I don't have a MySQL environment or intimate familiarity with it to allow me to write or adapt queries off the top of my head (as I'm doing here), but I hope this will illustrate the structure of a solution for you in SQL Server syntax.
In terms of the answer I link to (which generates a date table on the fly) and extending it by adding in your holiday table (and making some inferences about how you've defined your holiday table), and noting that a working day is any day Mon-Fri that isn't a holiday, you'd write a query like so to get the number of working days between any two dates:
WITH
dynamic_date_table AS
(
SELECT *
FROM generate_series_datetime2('2000-01-01','2030-12-31',1)
CROSS APPLY datetime2_params_fxn(datetime2_value)
)
,date_table_ext1 AS
(
SELECT
ddt.*
,IIF(hol.dates IS NOT NULL, 1, 0) AS is_company_holiday
FROM
dynamic_date_table AS ddt
LEFT JOIN
tbl_holiday AS hol
ON (hol.dates = ddt.datetime2_value)
)
,date_table_ext2 AS
(
SELECT
*
,IIF(is_weekend = 1 OR is_company_holiday = 1, 0, 1) AS is_company_work_day
FROM date_table_ext1
)
SELECT
COUNT(datetime2_value)
FROM
date_table_ext2
WHERE
(datetime2_value BETWEEN '2018-02-14' AND '2018-02-20')
AND
(is_company_work_day = 1)
Obviously, the idea for a well-factored solution is that these intermediate calculations (being general in nature to the entire company) get rolled into the date_params_fxn, so that any query run against the database gains access to the pre-defined list of company workdays. Queries that are run against it then start to resemble plain English (rather than the approach you linked to and adapted in your question, which is ingenious but far from clear).
If you want top performance (which will be relevant if you are hitting these calculations heavily) then you define appropriate parameters, save the lot into a stored date table, and index that table appropriately. This way, your query would become as simple as the final part of the query here, but referencing the stored date table instead of the with-block.
The sequentially-numbered workdays I referred to in my comment on your question, are another step again for the efficiency and indexability of certain types of queries against a date table, but I won't complicate this answer any further for now. If any further clarification is required, please feel free to ask.

Answer 2

I found the answer for this problem
It turns out, I just need to use a simple arithmetic operator for this problem
SELECT (SELECT DATEDIFF('2018-02-20', '2018-02-14')) - (SELECT COUNT(id) FROM tbl_holiday WHERE dates BETWEEN '2018-02-14' AND '2018-02-20');