MySQL回合怪异的bug [英] MySQL round weird bug

问题描述

我正面临着一个非常奇怪的错误?在mysql + php上. 是一个简单的选择，在下面的示例中，我使用多个字段来尝试解释我的问题:

I'm facing a really weird ¿bug? on mysql+php right now. Is a simple select, in the following example i'm using multiple fields to try to explain my problem:

• 字段"为11.5
• $ phpvar为1.15

MySQL查询:

select round(field * " . $phpvar . " ,2) as a1, 
       round(field * 1.15 ,2) as a2, 
       round(11.5 * " . $phpvar . " ,2) as a3, 
       round(11.5 * 1.15 ,2) as a4, 
       field * " . $phpvar . " as a5 
from ...

好的，我正在尝试获得13.23. "field" * $phpvar = 13.225，所以使用round(13.225,2)我应该得到13.23，对吧?好，是的，不是.

ok, i'm trying to get 13.23. "field" * $phpvar = 13.225, so using round(13.225,2) I should get 13.23, right? well, yes and no.

查询结果:

• a1 [round(field *.$ phpvar."，2)] => 13.22
• a2 [round(field * 1.15，2)] => 13.22
• a3 [round(11.5 *.$ phpvar."，2)] => 13.23
• a4 [round(11.5 * 1.15，2)] => 13.23
• a5 [field *.$ phpvar."] => 13.225(无回合)

我想念什么?在使用字段"时，我的结果怎么可能会假一轮?

what am I missing? how is it possible, when it comes to use "field", my result gets a fake round?

推荐答案

问题是如何存储DOUBLE和FLOAT值.

The problem is how the DOUBLE and FLOAT values are stored.

可能(也可能)将11.5或22.475 coul的值存储在近似值(如11.499999999999〜或22.475000000000000001)中，因此某些计算或四舍五入可能导致错误的结果.

It is possible (and probable) that values like 11.5 or 22.475 coul be stored in approximated values like 11.499999999999~ or 22.475000000000000001 thus some calculations or roundings could lead to incorrect results.

始终最好将浮点值存储为 DECIMAL 列明类型，在该类型中，该值应与所有十进制数字完全存储在一起，而不是近似值.

It is always better to store float values into a DECIMAL coulmn type where the value is stored exactly with all the decimal digits and is not approximated.

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