Result of DIV with Decimal and Integer 重要bug

sunwy

最近几天在使用php+mysql 设置一个程序时，发现一个奇怪的问题

在mysql里面使用div，也就是取模函数
900 div 500  结果=1

但
900.00 div 500 结果居然等2
接着测试
749.00 div 500 =1
750.00 div 500 =2


天这是什么逻辑，让我反复检查了近一个小时的程序代码，发现居然错在这里。
我的mysql版本是：5.5.12，看官方的说明，似乎是5.5.16以后版本才修复了这个bug

下面是官方资料：
[28 Jun 2011 15:54] Jun Yao
Description:(5 DIV 2) and (5.0 DIV 2) results in different values.  This is not the same behavior in MySQL 5.0 version, in which results seem to make more sense.How to repeat:SELECT 5 DIV 2;Result = 2SELECT 5.0 DIV 2;Result = 3Suggested fix:Since the documentation states that DIV is similar to FLOOR, after the decimal division, maybe FLOOR should be used instead of rounding to the nearest integer.
[28 Jun 2011 16:00] Jun Yao
In 5.1, results are also consistent.  Both (5.0 div 2) and (5 div 2) equal 2.
[29 Jun 2011 7:13] Valeriy Kravchuk
Thank you for the bug report. Verified just as described. Looks like regression comparing to 5.1.x.
[24 Sep 2011 16:48] Paul DuBois
Noted in 5.5.16, 5.6.3 changelogs.(5 DIV 2) and (5.0 DIV 2) produced different results (2 versus 3)because the result of the latter expression was not truncated beforeconversion to integer. This differed from the behavior in MySQL 5.0and 5.1. Now both expressions produce 2.


该贴已经同步到 sunwy的微博