mysql - 为什么这些总数不匹配

Question

我需要计算税金和折扣。这是我正在使用的公式，但查询返回很短。

((8.75+0)/100)*(50.00*1 - (50*1*.1/100)) as test,

MySQL 返回 4.370625，当我在计算器上计算 (0.0875 * 50 - 0.05) 时，我得到:3.875

我哪里错了？

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让我们以这个真实世界为例

A single item for sale:
Quantity:  1.00
Price: $20.00
Tax: 8.75%
Discount: 10%

The tax should equal: $1.58
The subtotal without tax is $18.00
Total: $19.58 (after the discount and tax added)

如何编写查询以获取税金并单独计算以获取折扣？

Answer 1

你应该做 0.0875 * (50 - 0.05)。先差后乘。

((8.75+0)/100)*(50.00*1 - (50*1*.1/100))

( 8.75   /100)*(50      -  0.05        )

  0.0875      *(50      -  0.05        )

  0.0875      * 49.95

  4.370625

你的真实例子(如果所有数字都像这里):

A single item for sale:
Quantity:  1.00
Price: $20.00
Tax: 8.75%
Discount: 10%


"Total Tax" = Quantity * (Price * (1. - (Discount / 100.)) * (Tax / 100.)
"Subtotal without tax" = Quantity * (Price * (1. - (Discount / 100.))
"Total" = Quantity * (Price * (1. - Discount / 100.) * (1. + Tax / 100.))