Question

I need to fetch all records from current week. But since Monday Dec 31st was in 2012, mysql treats it as week 53, instead of week 1 of 2013. How can I get around that?

Query:

SELECT COUNT(*) AS `cnt`
FROM `orders`
WHERE WEEK(`date_purchased`, 1) = WEEK(NOW(), 1)
    AND (
           (
            MONTH(`date_purchased`) = MONTH(NOW() - INTERVAL 1 WEEK)
            AND YEAR(`date_purchased`) = YEAR(NOW() - INTERVAL 1 WEEK)
            )
        OR (
            MONTH(`date_purchased`) = MONTH(NOW())
            AND YEAR(`date_purchased`) = YEAR(NOW())
            )
        )

Answer 1

According to ISO standard, week number 1 of the year is the first week with the majority of its days in the starting year, and while week(date,1) returns week 53 for ‘2012-12-31’, week(date,3) or its equivalent weekofyear(date) correctly return week number according to this standard, so:

weekofyear('2013-01-01') = weekofyear('2012-12-31') = 1
-- week starts on Monday, and 2012-12-31 is part of the first week of 2013

weekofyear('2012-01-01') = weekofyear('2011-12-31') = 52
-- last week of 2011 starts on 12-26, first week of 2012 starts on 01-02

weekofyear('2010-01-01') = weekofyear('2009-12-31') = 53
-- some years have 53 weeks

weekofyear('2007-01-01') != weekofyear('2006-12-31')
-- that's correct because the first day of 2007 was a Monday

Since your request is more specific, if you have to check if two days are part of the same week of the same year, this is still not enough to answer your question.

Instead of using week, or weekofyear, it’s better to use yearweek(date,mode) function, using mode=3, that returns the same week numbers as above, but also preceded by the year this week refers to:

yearweek('2013-01-01', 3) = yearweek('2012-12-31', 3) = 201301
yearweek('2012-01-01', 3) = yearweek('2011-12-31', 3) = 201152
yearweek('2010-01-01', 3) = yearweek('2009-12-31', 3) = 200952
yearweek('2007-01-01', 3) != yearweek('2006-12-31', 3)

so your query could become:

SELECT COUNT(*) AS `cnt`
FROM `orders`
WHERE YEARWEEK(`date_purchased`, 3) = YEARWEEK(DATE(), 3)