#TIL 13ths are more often Fridays than other weekdays:
select extract(dow from d), count(*) from generate_series(date 'today' - interval '400 years', date 'today' + interval '400 years', interval '1 day') as g(d) where extract(day from d) = 13 group by 1 order by 1;
@PostgreSQL
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“a 400-year cycle not only starts 2000-03-01 (as it did 1600-03-01), it contains an even number of weeks: 20,871.” My all time favorite reference for understanding the calendar is at http://naggum.no/lugm-time.html
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Yeah, he wrote a lot of really great stuff. I read all of that when I was at my Lisp peak and trying to write a time library for Emacs: https://github.com/macdice/protocolarium/blob/master/clock.el … (man, I really should come back and finish that, I still spend most of my time in Emacs and frequently tangle with TZs)
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