From: Daevid Vincent
Date: August 4 2006 7:20am
Subject: Calculating birthdays and distances... Is there a bug?
List-Archive: http://lists.mysql.com/mysql/200616
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I posted this as a comment on the page too, but I=92m curious as to why =
the
top solution is off by a day or so... Is this a bug or a rounding issue =
or
what? Is there a way to "fix" the top one to work the way I expect/want =
it
to work? I suspect it's because (as Jack Palance said in 'City =
Slickers')
"the day ain't over yet" that I get the rounding error.

http://dev.mysql.com/doc/refman/5.1/en/date-and-time-functions.html

SET @DOYNOW =3D DAYOFYEAR(CURDATE());

SELECT (DAYOFYEAR(birthdate) - @DOYNOW) AS birthdays, birthdate, =
@DOYNOW,
CURDATE()=20
FROM users
WHERE birthdate IS NOT NULL;

then if birthdays =3D=3D 0, it's that persons birthday, otherwise you =
know if
the birthday is in the future by how many days, or if you missed it and =
how
many beers you owe them...

(although the missed/negative days seems to be off)

+-----------+------------+---------+------------+
| birthdays | birthdate  | @DOYNOW | CURDATE()  |
+-----------+------------+---------+------------+
|        83 | 1969-10-26 | 216     | 2006-08-04 |=20
|         3 | 1981-08-07 | 216     | 2006-08-04 |=20
|        -1 | 1972-08-02 | 216     | 2006-08-04 |=20
|         0 | 1946-08-04 | 216     | 2006-08-04 |=20
|      -151 | 1976-03-05 | 216     | 2006-08-04 |=20
+-----------+------------+---------+------------+

Shouldn't that -1 be -2 ?
Am I missing something obvious?

If I do "SELECT DATEDIFF('2006-08-01', CURDATE());" I get -2 as I =
expect.

So, I guess the real solution is to use this:

SET @YEAR =3D CONCAT(EXTRACT(YEAR FROM CURDATE()),'-');

SELECT DATEDIFF(CONCAT(@YEAR, DATE_FORMAT(birthdate, '%m-%d')), =
CURDATE())
AS birthdays, birthdate, CURDATE()=20
FROM users
WHERE birthdate IS NOT NULL;

+-----------+------------+------------+
| birthdays | birthdate  | CURDATE()  |
+-----------+------------+------------+
|        83 | 1969-10-26 | 2006-08-04 |=20
|         3 | 1981-08-07 | 2006-08-04 |=20
|        -2 | 1972-08-02 | 2006-08-04 |=20
|         0 | 1946-08-04 | 2006-08-04 |=20
|      -152 | 1976-03-05 | 2006-08-04 |=20
+-----------+------------+------------+

By the way, if you're using PHP or some other scripting language, you =
can
get rid of the @YEAR stuff and just do:

DATEDIFF(DATE_FORMAT(birthdate, '".date('Y')."-%m-%d'), CURDATE()) AS
birthdays

=D0=C65=CF=D0=20