The relations between integer division, remainder, and modulus are
illustrated by the following table:
A B A/B A rem B A mod B A B A/B A rem B A mod B
10 5 2 0 0 -10 5 -2 0 0 11 5 2 1 1 -11 5 -2 -1 4 12 5 2 2 2 -12 5 -2 -2 3 13 5 2 3 3 -13 5 -2 -3 2 14 5 2 4 4 -14 5 -2 -4 1
10 -5 -2 0 0 -10 -5 2 0 0 11 -5 -2 1 -4 -11 -5 2 -1 -1 12 -5 -2 2 -3 -12 -5 2 -2 -2 13 -5 -2 3 -2 -13 -5 2 -3 -3 14 -5 -2 4 -1 -14 -5 2 -4 -4
PB
Jigal van Hemert wrote:
From: "Thomas Lenherr"
Hi Thomas,
I just wanted to know if there is a special reason for the mathematically incorrect implementation of the modulo-operation in mysql. Using a correct modulo operation on a negative number would still result in a positive number: -1 % 2 == 1 (mysql: -1) -5 % 3 == 1 (mysql: -2) -1 % 4 == 3 (mysql: -1)
(For the exact definition see http://en.wikipedia.org/wiki/Modulo_operation )
AFAIK most programming languages implement modulo in this wrong way
(except pascal i think), but I don't have a clou why it should stay that
way as I find this behaviour rather disturbing...
I don't see any difference between the wikipedia definition and the MySQL implementation, especially since the article mentions that "what exactly constitutes the result of a modulo operation depends on the programming language and/or the underlying hardware."
In the MySQL manual the results for negative numbers are not mentioned, nor defined.
IMHO the examples you mention give correct results with MySQL: -1 / 2 = 0 remains: -1 -5 / 3 = -1 remains: -2 -1 / 4 = 0 remains: -1
Regards, Jigal.
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