Repeating calendar events and some final maths - mysql

Question

I am trying to have a go at the infamous repeating events on calendars using PHP/MySQL. I've finally found something that seems to work. I found my answer here but I'm having a little difficulty finishing it off.
My first table 'events'.
ID NAME
1 Sample Event
2 Another Event
My second table 'events_meta that stores the repeating data.
ID event_id meta_key meta_value
1 1 repeat_start 1336312800 /* May 7th 2012 */
2 1 repeat_interval_1 432000 /* 5 days */
With repeat_start being a date with no time as a unix timestamp, and repeat_interval an amount in seconds between intervals (432000 is 5 days).
I then have the following MySQL which I modified slightly from the above link. The timestamp used below (1299132000 which is 12th May 2012) is the current day with no time.
SELECT EV.*
FROM `events` EV
RIGHT JOIN `events_meta` EM1 ON EM1.`event_id` = EV.`id`
RIGHT JOIN `events_meta` EM2 ON EM2.`meta_key` = CONCAT( 'repeat_interval_', EM1.`id` )
WHERE EM1.meta_key = 'repeat_start'
AND (
( CASE ( 1336744800 - EM1.`meta_value` )
WHEN 0
THEN 1
ELSE ( 1336744800 - EM1.`meta_value` ) / EM2.`meta_value`
END
)
) = 1
In the above MySQL, the following code deducts the repeat_start field (EM1.'meta_value') from the current date and then divides it by the repeat interval field (EM2.'meta_value').
ELSE ( 1336744800 - EM1.`meta_value` ) / EM2.`meta_value`
OR
TODAYS DATE - START DATE / 5 DAYS
So here's the maths:
1336744800 - 1336312800 = 432000
432000 / 432000 = 1
Now that works perfect. But if I change the current timestamp 5 days ahead to 1336312800 which is 17th Mat 2012, it looks a bit like this:
1336312800 - 1336312800 = 864000
86400 / 432000 = 2
Which doesn't work because it equals 2 and in the MySQL it needs to equal 1. So I guess my question is, how do I get the MySQL to recognise a whole number rather than having to do this?
...
WHERE EM1.meta_key = 'repeat_start'
AND (
( CASE ( 1336744800 - EM1.`meta_value` )
WHEN 0
THEN 1
ELSE ( 1336744800 - EM1.`meta_value` ) / EM2.`meta_value`
END
)
) = IN (1,2,3,4,5,6,7,8,....)
Hope I'm making sense and I hope it's just a simple maths thing or a function that MySQL has that will help :) Thanks for your help!
EDIT: THE ANSWER
Thanks to #eggypal below, I found my answer and of course it was simple!
SELECT EV.*
FROM elvanto_calendars_events AS EV
RIGHT JOIN elvanto_calendars_events_meta AS EM1 ON EM1.`event_id` = EV.`id`
RIGHT JOIN elvanto_calendars_events_meta AS EM2 ON EM2.`meta_key` = CONCAT( 'repeat_interval_', EM1.`id` )
WHERE EM1.meta_key = 'repeat_start'
AND ( ( 1336744800 - EM1.`meta_value` ) % EM2.`meta_value`) = 0

Answer 1

It's not entirely clear what you want your query to do, but the jist of your question makes me lean toward suggesting that you look into modular arithmetic: in SQL, a % b returns the remainder when a is divided by b - if there is no remainder (i.e. a % b = 0), then a must be an exact multiple of b.
In your case, I think you're trying to find events where the time between the event start and some given literal is an exact multiple of the event interval: that is, (literal - event_start) % event_interval = 0. If it's non-zero, the value is the time to the next occurrence after literal (and, therefore, to determine whether that next occurrence occurs within some period of time, say a day, one would test to see if the remainder is less than such constant e.g. (literal - event_start) % event_interval < 86400).
If this isn't what you're after, please clarify exactly what your query is trying to achieve.

Answer 2

set #dat_ini = '2023-05-20',#dat_fim = '2022-11-20'; select (DATEDIFF( #dat_fim,#dat_ini )) % 60
THIS < 10
It only works for a short period.
To do this, take the start date and change the Month that is on the screen and add a year, then subtract it from the start date, then it works.