DATEDIFF in MySQL with ranges extending new year - mysql

Question

I have a database table with holiday requests in it. I now want to calculate, how many days the user has requested for a certain year. So far I did this:
Table:
CREATE TABLE `holidays` (
`id` int(11) NOT NULL,
`user` int(11) NOT NULL,
`begin` date NOT NULL,
`end` date NOT NULL,
`comment_user` text NOT NULL,
`entered_at` int(11) NOT NULL
) ENGINE=MyISAM DEFAULT CHARSET=utf8;
Get all holidays in a year:
SELECT SUM((DATEDIFF(end, begin) + 1)) AS days
FROM holidays
WHERE user = :user AND begin LIKE '2021%'
But what can I do, if begin date is in the year before (e.g. 12/30/2020) or end date is in the next year (e.g. 01/05/2022), so the request extends over new year's eve.
EXAMPLE:
If I have a holiday request from 12/30/2020 to 01/02/2021, I wanna count just two days of that, not all four days.
Only the days in 2021
Is there any possibilty to limit the DATEDIFF calculation to 01/01/2021 AND 12/31/2021, but getting all requests affected in that year?
And how can I put that in one mysql-query? I can't find any solution on google for that.
Would be great, if someone had a similar problem and solved that.
Thank's in advance,
Tobias

Answer 1

I created a sample database like this (FIDDLE):
CREATE TABLE `holidays` (
`begin` date DEFAULT NULL,
`end` date DEFAULT NULL
)
INSERT INTO `holidays` VALUES
('2020-12-28','2021-01-05'),
('2020-12-05','2020-12-06'),
('2021-01-06','2021-01-06');
This SQL-statement:
select
begin,
CASE WHEN year(end)>year(begin) then ADDDATE(makedate(year(`end`),1),INTERVAL -1 DAY) else `end` end as END ,
year(begin) as year
from holidays
union all
select
makedate(year(`end`),1),
`end`,
year(`end`)
from holidays
where year(`begin`)<>year(`end`);
will have as output:
+------------+------------+------+
| begin | END | year |
+------------+------------+------+
| 2020-12-28 | 2020-12-31 | 2020 |
| 2020-12-05 | 2020-12-06 | 2020 |
| 2021-01-06 | 2021-01-06 | 2021 |
| 2021-01-01 | 2021-01-05 | 2021 |
+------------+------------+------+
BTW: One should never use, or at least try to avoid, reserved words in a table definition (like 'begin', 'end')