MYSQL Interval - Same day of the week one year in the future - mysql

Question

Does anyone have a snippet of MYSQL code that will give me the new datetime of a day one year in the future that is the same day of the week?
SELECT new_day = ADDDATE(new_day,INTERVAL 364 DAY) FROM my_table
Works on non-leap years. Any ideas how to deal best with leap years?

Answer 1

Given that a normal year is 52 weeks and 1 day long and a leap year is 52 weeks and 2 days long, your new date will be one or two days earlier in the year than it was in the old year. For any date after New Year's Day in a regular year, or any date after the 2nd of January in a leap year, adding 52 week or 364 days gives you a date in the next year that is on the same day of the week and occurs 1 or 2 days earlier in the month (or at the end of the prior month).
That leaves you with the problem of what to do with the first two days of the year. Presumably 'next year' is crucial, so the simple answer that 2013-12-31 is 52 weeks later than 2013-01-01 is not OK. In this case, you have to write a conditional expression, spelled CASE in SQL.
SELECT CASE WHEN YEAR(DATEADD(ref_date, INTERVAL 364 DAY)) = YEAR(ref_date)
THEN DATEADD(ref_date, INTERVAL 371 DAY)
ELSE DATEADD(ref_date, INTERVAL 364 DAY)
END
FROM ...wherever...

Answer 2

how do you wish it to deal with leap years? either save month and date and compare if 364 or 371 are closest to first day, and pick regardingly, or do nothing and face inaccuracy after a couple of years.
*saved_date* is the very first date before created new dates based on it
*passed_years* is increasing for every new since the first
date_add(last_date, INTERVAL (case when datediff(date_add(saved_date, INTERVAL passed_years YEAR), date_add(last_date, INTERVAL 371 DAY)) <= 3 then 371 else 364 end)) DAY)
The idea of this is to either fetch 52 or 53 weeks of the next year. leap years doesn't affect weekdays, but they "contribute" to an already existing problem; the date gets lower for each passing year if you only add 52 weeks each year without above solution.

Answer 3

Why not simply
CURDATE() + INTERVAL 52 WEEK`
Sure, it will be 1 or 2 days earlier in the 'calendar'.
mysql> SELECT NOW(), CURDATE() + INTERVAL 52 WEEK;
+---------------------+------------------------------+
| NOW() | CURDATE() + INTERVAL 52 WEEK |
+---------------------+------------------------------+
| 2017-09-05 15:50:46 | 2018-09-04 |
+---------------------+------------------------------+
If you need it to be 'later', then use 53.