If week months were defined to begin on the nearest Monday to the first day of the Gregorian month, or, in other words, weeks belonged to the calendar month the majority of their days and thus their Thursday are in, then seemingly irregular patterns would be the result.
Many ordinal weeks would always be in the same month, but some would fluctuate between two months. Months could also be assigned regularly to the weeks, but the months of such a mapping will deviate from the Gregorian months by more days. Each equinox and solstice varies over a range of at least seven days.
This is because each equinox and solstice may occur any day of the week and hence on at least seven different ISO week dates. For example, there are summer solstices on W and W It cannot replace the Gregorian calendar , because it relies on it to define the new year day Week 1 Day 1. There are 13 Julian year subcycles with 5 leap years each, and 6 remaining leap years in the remaining 36 years the absence of leap days in the Gregorian calendar in , , and interrupts the subcycles.
The leap years are 5 years apart 27 times, 6 years 43 times and 7 years once. A slightly more even distribution would be possible: 5 years apart 26 times and 6 years 45 times. The Gregorian years corresponding to the 71 long, ISO leap-week years can be subdivided as follows:.
Thus 27 ISO years are 5 days longer than the corresponding Gregorian year, and 44 are 6 days longer. Of the other Gregorian years neither starting nor ending with Thursday , 70 are Gregorian leap years, and are non-leap years, so 70 week years are 2 days shorter, and are 1 day shorter than their corresponding month years.
The best leap week calendars to convert to Gregorian would be those based on the ISO week or a similar week numbering scheme. Karl Palmen thought of another that interlocks with the year subcycle that such calendars have, which is interrupted by a dropped leap day in three out of four century years. In each row, the leap years are six years apart and the first of each row is four years after the last of the previous row. Each row covers 28 years unless it contains a dropped Gregorian leap day, in which case it covers 40 years.
The rows are synchronized to the year cycles that occur in any week-number calendar like ISO week date. In particular, the 2nd year of each row is a leap year starting on Tuesday GF. A simpler leap week rule would have rows alternating between 28 and 34, but this would be harder to convert to and from the Gregorian calendar.
The following variation, offset by 12 years, matches all even-numbered years with 53 ISO weeks. Gregorian leap years are shown in bold. Many retail and financial systems divide ISO Quarters into three segments of weeks, though other segment systems also exist. Open Tableau Desktop and connect to the Sample-Superstore saved data source.
Set ISO as the default calendar. In a segment calendar, each quarter is divided into 3 segments with 4 or 5 weeks in them. We must find how many weeks are in each quarter in order to divide them into segments. Dates and Times Link opens in a new window. Date Functions Link opens in a new window. Tableau Desktop and Web Authoring Help. Version: ISO Week Numbers start at "1" so it would seem that just adding "1" to the answer would do the trick.
Ah, but wait. If we add "1" to that, would start off at a week number of "2" and as a good friend of mine once said, "That ain't right". You could go through a bunch of gyrations to figure out that if that first week has a value of "7" that you wouldn't add "1". Instead, let's once again consider the miracle of Integer Math. If we add 6 days to the Date Serial Number before we do the division, it's like adding. So, the "7" would become "13".
In Integer Math, the remainder is simply dropped so we'd end up with the correct answer of "1". Let's look at the opposite end of the spectrum. As we've already seen, that would also result in the correct answer of "1".
Looking at the end of , we see the Thursday of that week was also the last day of the year or It all works correctly for everything in between, as well. We already have this formula in all of the code that we posted.
Again, the final formula is listed in this next snippet of code, which is what we started out to begin with. Look carefully at the formula. No where did we violate such a rule. We divided that number by 7, multiplied it by 7, and added 3 to it. That was all Integer Math. We then took that Integer, added 6 to it and divided it by 7. If you know me, you just had to know a million row test was coming next. Here's the code for the whole shootin' match. The code calculates the answers and dumps the results to a variable to take the display times out of the picture.
Here are the results from SQL Profiler. The duration is in milliseconds, just to keep things simple. Doing the math to take the average duration of each method, we end up with a difference of only 34 milliseconds difference between the two… on a million rows. I should probably change my name to "Lumpy" because I'm still banging my head about missing such an elegantly simple and very high performance formula myself all these years.
It can easily be turned into either a Scalar ugh! User Defined Function or into a much higher performance iSF. If you really want to show your appreciation, we could all join together and bang our heads hard enough so he can hear it all the way over in Denmark.
Log in or register to rate. Join the discussion and add your comment. Sometimes you need to output blank lines - in effect displaying Records for Missing Data. This article explains how to use a CTE to do this.
Sometimes we need to break down a complex problem into a multiple stage solution to achieve optimal performance. In this sequel to his first "Hierarchies on Steroids" article, SQL Server MVP Jeff Moden shows us how to build a pre-aggregated table that will answer most of the questions that you could ask of a typical hierarchy.
Correction - 23 Nov I've made no changes in the article starting with the "Introduction" because it still correctly describes the original formula written by "t-clausen. I had the article taken "offline" until I could fix it and test it. TestTable ; Like I said, it's absolutely brilliant and my mathematical hat is off to by t-clausen. Generating Test Dates in a Table Before we can tear the formula apart and see how it works, we need to make some dates to test with.
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