mysql - 有趣的 sql 查询(不在 select 中)

Question

我在 mysql 中有以下 sql 查询:

SELECT * 
FROM _t_test
WHERE pret NOT 
IN ( 2.6700, 2.6560, 1.8200 ) 

我希望不会显示值为 1.8200 的行，但我仍然得到它们。我错过了什么吗？“pret”字段是 double(16,4)。

Answer 1

这是一个舍入误差。 double 不是精确值，因此 1.8200 未准确表示，因此值不完全相同。

对于 MYSQL float ，请参阅 http://dev.mysql.com/doc/refman/5.0/en/problems-with-float.html

The correct way to do floating-point number comparison is to first decide on an acceptable tolerance for differences between the numbers and then do the comparison against the tolerance value. For example, if we agree that floating-point numbers should be regarded the same if they are same within a precision of one in ten thousand (0.0001), the comparison should be written to find differences larger than the tolerance value

参见 http://en.wikipedia.org/wiki/Double_precision_floating-point_format