存储在MySQL中的浮点值不断变得混乱 [英] Float value stored in MySQL keeps getting messed up

问题描述

我试图在MySQL中存储浮点值，我的值似乎不断变得混乱。 :(

$ b $我有我的领域定义为浮动（10,7）和我在我的值正确的PHP插入之前：

（b

$ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $' / code>

但是当我插入一个值如47.5206797，它在我的表中显示为47.520679 5 。为什么会这样？

解决方案

如果您需要精确的值，请将其存储为精确的数据类型，如 DECIMAL（17,7），它将提供与 FLOAT（10,7）相同的范围。唯一的缺点是那么 DECIMAL 会占用比equivilant FLOAT 更多的磁盘空间，但是与校正浮点数相比，这是微不足道的错误，其中精度是一个问题。

http://dev.mysql.com/doc/refman/5.0/en/fixed-point-types.html

佛有关浮点数问题的更多信息，以下内容可能值得一读

http://dev.mysql.com/doc/refman/5.0/en/problems-with-float.html

I'm trying to store float values in MySQL and my values seem to keep getting messed up. :(
I have my fields defined as float(10,7) and I round my values properly in PHP before inserting them:

$rndval = round($val,7)
INSERT INTO mytable (float) VALUES ($rndval)

But when I insert a value such as 47.5206797, it shows up as 47.5206795 in my table. Why is that?

解决方案

If you need a value to be precise, store it as an exact data type such as DECIMAL(17,7), which would provide the same range as FLOAT(10,7). The only down side is that the DECIMAL will take up more disk space than the equivilant FLOAT, however this is trivial compared to correcting for floating point errors where precision is a concern.

http://dev.mysql.com/doc/refman/5.0/en/fixed-point-types.html

For more information on floating point number issues, the following may be worth a read

http://dev.mysql.com/doc/refman/5.0/en/problems-with-float.html

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