Question

I’m working on a reporting system using Java 6 and SQL Server 2008. For some queries I want to look at the data by week number. I’m using Java to fill in gaps in the the data to make a continuous time line and I have found that

java.util.Calendar cal = new java.util.GregorianCalendar();
cal.set(2012, 0, 1);
cal.get(Calendar.WEEK_OF_YEAR);

and

org.joda.time.DateTime date = new org.joda.time.DateTime(2012, 01, 01, 0, 0);
date.getWeekOfWeekyear();

return a different week number to

DATEPART(WEEK, '2012-01-01')

Is there an approach to resolving this difference or will I have to choose to use SQL Server or Java week numbers?

TIA

Answer 1

Java is more sophisticated when it comes to calculating week numbers, whereas SQL-Server DATEPART(WEEK… is more simplistic. I found the following documented here

“When setting or getting the WEEK_OF_MONTH or WEEK_OF_YEAR fields, Calendar must determine the first week of the month or year as a reference point. The first week of a month or year is defined as the earliest seven day period beginning on getFirstDayOfWeek() and containing at least getMinimalDaysInFirstWeek() “

I think this defaults to the ISO standards which is the first week of the year with a thursday in (Monday-Sunday weeks where at least 4 days are the year). Consider using:

In SQL Server the DATEPART(WEEK, ..) function is much more simplistic, it simply calculates the number of week boundaries (as defined by DATEFIRST) between the first of january, and the input date, so the 1st January will always be week 1. You may wish to consider using:

SELECT DATEPART(ISO_WEEK, '01/01/2012')

This gets the week number as defined by the ISO standards, which is the first week of the year with a thursday in (Monday-Sunday weeks where at least 4 days are the year).

Since, as stated SQL Server is more simplistic in it’s calculations, this can’t be configured, which means that you will need to configure your week numbers within Java. Simply ensure you set up your calendar in Java with the correct values for getFirstDayOfWeek() and getMinimalDaysInFirstWeek():

public static Calendar getISOCalendar() {
    Calendar calendar = Calendar.getInstance();
    calendar.setMinimalDaysInFirstWeek(4);
    calendar.setFirstDayOfWeek(Calendar.MONDAY);
    return calendar;
}

Then you can esnsure consistent week numbers.

public static void main(String args[]) {
    Calendar calendar = getISOCalendar();
    calendar.set(2012,0,1);
    System.out.println(calendar.get(Calendar.WEEK_OF_YEAR));
}

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