How Do I Calculate the Number of the Following Week? - php

Question

I need to calculate the number of the week following a given week. This is trivial for most weeks within the year, but not at the end / beginning of the year. For example if I need to know the week following week 52 of 2013.
I would like to use the defaul_week_format 3, i.e.
a) the weeks start with Monday (instead of Sunday)
b) the numbering within a year starts with 1 (instead of 0)
and c) week number 1 is the first week with more than 3 days this year.
My approach to e.g. calculate the week after week 36 2014 is the following:
SELECT WEEK(DATE_ADD(STR_TO_DATE('W36 2014 Tuesday', 'W%V %X %W'), INTERVAL 1 WEEK))
For this example I calculate the date of Tuesday in week 36, add one week, and calculate the week of this day. This would work, but even without adding one week, I have this strange behaviour:
It works for the default_week_format 0:
SET ##local.default_week_format=0;
SELECT STR_TO_DATE('W36 2014 Tuesday', 'W%V %X %W');
-> Tuesday of week 36 is 2014-09-09
SELECT week('2014-09-09');
-> 2014-09-09 is in week 36
So far, so good: Tuesday of week 36 is in week 36.
But this simple experiment does NOT work for default_week_format 3:
SET ##local.default_week_format=3;
SELECT STR_TO_DATE('W36 2014 Tuesday', 'W%V %X %W');
-> Tuesday of week 36 is 2014-09-09
-> This is wrong, because numbering should start with 1 (instead of 0 now)!
-> Tuesday of week 36 should be 2014-09-02
SELECT week('2014-09-09');
-> 2014-09-09 is in week 37
So MySQL tells me that Tuesday of week 36 is in week 37!
My only explanation for this:
week() takes default_week_format into account
str_to_date() ignores the default_week_format
How can I force MySQL function str_to_date to use the default_week_format?
Or: How else can I calculate the number of the following week?
I could also do it in PHP, but I get the weeks' numbers from a MySQL database.
Thanks for any help!

Answer 1

I was facing exactly the same problem. My solution - perhaps not the greatest one, but it works.
As you already mentionned: Most of the cases are trivial, you just need to know the year end / beginning. Therefore, I just store the relevant weeks for the needed number of years in the following table:
CREATE TABLE `NEXT_WEEK_TAB` (
`CUR_WEEK` varchar(8) NOT NULL,
`NEXT_WEEK` varchar(8) NOT NULL,
PRIMARY KEY (`CUR_WEEK`,`NEXT_WEEK`)
)
You get the following week now with the current algorithm:
following_week = (SELECT next_week
FROM next_week_tab
WHERE cur_week = <your_current_week>);
if !following_week then following_week++;
As I said: Probably not the nicest solution, but it's pretty simple - and it works.

Answer 2

I think you must use Week with a mode argument
mysql> SELECT WEEK('2008-02-20',0);
-> 7
mysql> SELECT WEEK('2008-02-20',1);
-> 8
take a look here :
http://dev.mysql.com/doc/refman/5.5/en/date-and-time-functions.html#function_week