On Mon, Dec 1, 2014 at 5:45 PM, Booth Martin <booth@xxxxxxxxxxxx> wrote:
If one is comparing sales by weeks and the first week is 2 days long and the
last week is 6 or 9 days long the results are skewed. Unless I misunderstood
how your intent? (Which is entirely possible - way too often it takes me
a few tries to finally grasp what was intended.)

Well, I don't know of any system where the last week (or any week) is
9 days long. If you're talking about mixing ISO week numbers and
Gregorian calendar years, then yes, you can get short first and last
weeks. But ISO years are actually defined such that there is no
overlap, and every ISO week is exactly 7 days and belongs to exactly
one ISO year (there is no such thing as an ISO week that straddles two
ISO years).

This is precisely why Rob was thinking there ought to be a YEAR_ISO
function: because you can't use the Gregorian calendar year with ISO
week numbers.

As far as the "beauty" of using weeks for groupings because of their
consistency, and the necessity of being consistent when doing
comparisons for business purposes: Let me ask you, how do you
reconcile the fact that Christmas is sometimes Week 51 and sometimes
Week 52?

John Y.

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