MySQL 乘以浮点列：1*7.6 得到 7.599999904632568？

Question

当我查询 SELECT 1*7.6 时，它给了我 7.6

但是当我进行列乘法时 (products.commision*sold.amount):

SELECT *,
(products.commision*sold.amount) as fee
FROM sold
RIGHT JOIN products
ON sold.idprod=products.ID
AND DATE(sold.date) BETWEEN DATE('2015-10-01') AND DATE('2015-10-31')
WHERE sold.userid="1"
ORDER BY sold.userid

它给了我

ID | userid | date     | idprod | amount | Category | Name  | commision  | fee
60 | 1      | 15-10-01 | 21     | 1      | Volish   | Black | 7.6(float) | 7.599999904632568

为什么？

Answer 1

感谢您在评论中的帮助，

解决方案

浮点数是二进制，小数是...十进制，所以我将我的列更改为十进制(16,9)

Answer 2

在进行比较时，您必须将值类型转换为 integers/Decimals 而不是浮点数，因此

(CAST(products.commision AS Decimal(7,2)) * CAST(sold.amount AS Decimal(7,2))) as fee

来自 https://dev.mysql.com/doc/refman/5.0/en/cast-functions.html and casting a floating to decimal in mysql

小数点将值设置为7位最大大小和2位最大精度的小数(12345.67)

编辑：我不确定将 CAST 添加到原始值或简单地转换诸如

之类的答案是否更有效

(products.commision  * sold.amount ) as CAST(fee AS Decimal(7,2))

MySQL 乘以浮点列：1*7.6 得到 7.599999904632568？

MySQL Multiplying float columns: 1*7.6 gives 7.599999904632568?

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