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From:Martin Ramsch Date:August 3 1999 1:11pm
Subject:Re: How to do math with dates
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On Mo, 1999-08-02 14:47:53 -0400, John <siliconghost@stripped>
asked regarding date arithmetic.

As Paul already wrote, the maybe easiest way is to deal with numbers
of days only ...

And here's what happened with your queries:

> mysql> SELECT ROUND(((CURRENT_DATE-"1999-07-19")/7),0);
> +------------------------------------------+
> | ROUND(((CURRENT_DATE-"1999-07-19")/7),0) |
> +------------------------------------------+
> |                                  2855543 |
> +------------------------------------------+

In a numerical context (as is using a minus for substraction)
date and time functions give numerical results, too.
Thus CURRENT_DATE gives the number 19990802 is this case.

Strings used in a numerical context are automatically converted into
numbers as good as possible, thus "1999-07-19" resulting in the
number 1999.

Okay:  19990802-1999 = 19988803
       19988803 / 7  = 2855543.3
       ROUND(2855543.3,0) = 2855543

> Also, I tried entering the exact same thing as above, but I manually
> entered today's date.  This gave me 0 as an answer.  I don't quite
> understand that either.

You'll guess it now:  ROUND((1999-1999)/8),0) ...

Regards,
  Martin
-- 
Martin Ramsch <m.ramsch@stripped> <URL: http://home.pages.de/~ramsch/ >
PGP KeyID=0xE8EF4F75 FiPr=52 44 5E F3 B0 B1 38 26  E4 EC 80 58 7B 31 3A D7
Thread
How to do math with datesSilicon Ghost2 Aug
  • Re: How to do math with datesPaul DuBois2 Aug
  • Re: How to do math with datesMartin Ramsch3 Aug
  • Re: How to do math with datesChristian Mack3 Aug