在mysql中减去两个相等的值不为零 [英] Subtraction of two equal values is not zero in mysql

问题描述

为什么在mysql中将两个相等的值相减不等于零?

Why Subtraction of two equal values in mysql does not equal zero?

两个字段类型均为双精度.见下图

both field type are double. See image below

推荐答案

这称为近似精度.这不是错误，浮点数据类型旨在以这种方式工作.他们不能精确地存储数据.因此，如果这很重要，则应使用定点数据类型，例如

That's known as a approximate precision . This isn't an error, floating point data types are intended to work such way. They can not store data precisely. So if that matters, you should use fixed-point data types, such as DECIMAL in MySQL.

另一方面，您始终可以使用精度增量进行浮点比较，例如:

On the other hand, you can always use precision delta for comparisons for floating point, like:

SELECT 
  `foo`,
  `bar`,
  IF(ABS(`foo`-`bar`)<1E-13, 0, `foo`-`bar`) AS zero_compared
FROM
 t

如您所见，这里的增量是1E-13(通常就足够了)

as you can see, here delta is 1E-13 (normally, that will be enough)

这篇关于在mysql中减去两个相等的值不为零的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！