Group by weekofyear MySQL for the end of the year - mysql

Question

I need stats on orders, week by week, so I have done this:
SELECT YEAR(orders.date), WEEKOFYEAR(orders.date), COUNT(*)
FROM orders
GROUP BY YEAR(orders.date), WEEKOFYEAR(orders.date)
It worked for one year, but just now (new year) it does not count the last days of 53rd week (jan 1st, 2nd, 3rd). How can I update my Query in order to have the full last week (from Monday 2015-12-28 to Sunday 2016-01-03)?

Answer 1

You need to switch to YEARWEEK(orders.date,3) to get the ISO weeks as a single column. Using WEEK(orders.date,3) (which is exactly the same as WEEKOFYEAR) will return the correct week number, but YEAR(orders.date) will return either 2015 or 2016, splitting the week into four days in 2015 and and three days in 2016.

Answer 2

As Strawberry mentioned in the comments you're looking for the WEEK function. I just checked the documentation at the MySQL website.
Week(date [,mode])
This function returns the week number for date. The two-argument form of WEEK() enables you to specify whether the week starts on Sunday or Monday and whether the return value should be in the range from 0 to 53 or from 1 to 53. If the mode argument is omitted, the value of the default_week_format system variable is used
Here's an example
SELECT WEEK('2008-12-31',1);
=> 53
It should also be noted that this is not the same as the WEEKOFYEAR function.
Returns the calendar week of the date as a number in the range from 1 to 53. WEEKOFYEAR() is a compatibility function that is equivalent to WEEK(date,3).
We can see that the value of the mode parameter here is 3. Here is the table that shows the values for the modes
Mode First day of week Range Week 1 is the first week
0 Sunday 0-53 With a Sunday in this year
1 Monday 0-53 With 4 or more days this year
2 Sunday 1-53 With a Sunday in this year
3 Monday 1-53 With 4 or more days this year
4 Sunday 0-53 With a Sunday in this year
5 Monday 0-53 With 4 or more days this year
6 Sunday 1-53 With a Sunday in this year
7 Monday 1-53 With 4 or more days this year
Source
https://dev.mysql.com/doc/refman/5.0/en/date-and-time-functions.html#function_week

Answer 3

As I understand you, you want calculate total orders for one week only once not twice for various years.
I've written SQL query for SQL Server, but I think you can easy rewrite it on mysql.
DECLARE #test_table TABLE(created_date DATETIME, VALUE INT)
INSERT INTO #test_table
SELECT N'20151231', 10
UNION ALL
SELECT N'20151228', 20
UNION ALL
SELECT N'20160101', 40
UNION ALL
SELECT N'20160104', 5
UNION ALL
SELECT N'20160107', 2
SELECT first_day_week_number,
SUM(value) AS total
FROM
(SELECT *,
DATEPART(ww,
DATEADD(dd, -DATEPART(dw, created_date)+2, created_date)) AS first_day_week_number
FROM #test_table ) AS T
GROUP BY first_day_week_number
To avoid problems with years you could calculate first week day of order date and then get week number from it.