Rails 3-MySQL返回与Postgresql不同的结果 [英] Rails 3 - mysql returning different result than postgresql

问题描述

我正在尝试在查询中进行一些计算，我认为postgresql处理数学的方式与mysql不同，但我不确定区别在哪里.这是我从控制器发出的查询:

I am trying to do some calculations in my query and i think postgresql is handling the math differently than mysql is but i'm not sure where the difference is. This is my query from my controller:

Invoice.find(params[:id], :joins => :invoice_line_items, :select => "invoices.id, SUM(invoice_line_items.hours * invoice_line_items.rate) as subtotal, SUM(invoice_line_items.hours * invoice_line_items.rate) - (SUM(invoice_line_items.hours * invoice_line_items.rate) * (invoices.discount_percentage / 100)) as total", :group => "invoices.id")

在开发环境中，我使用mysql，在生产环境中，我使用postgresql.这些是我得到的输出.作为参考，Discount_percentage为20.

In my development environment i am using mysql and in my production environment i am using postgresql. These are the outputs that i am getting. For reference, the discount_percentage is 20.

MySQL:

 |  id  |  subtotal  |  total         |
----------------------------------------
 |  21  |  570.0000  |  456.00000000  |

PostgreSQL:

 |  id  |  subtotal  |  total         |
----------------------------------------
 |  9   |  570.0000  |  570.00000000  |

似乎与百分比和总数有关.有人有主意吗?顺便说一句，MySQL的结果就是我想要的.

It looks like it's something to do with the percentage and total. Anyone have any ideas? By the way, the MySQL result is what i am wanting.

推荐答案

Postgres正在执行整数除法.

Postgres is doing integer division.

Select                    MySQL   Postgres
-----------------------   -----   --------
select 999 / 100 as a     9.99    9
select 999 / 100.0 as a   9.99    9.99

因此，将 x/100 更改为 x/100.0 ，以使它们的行为相同.

So, change the x / 100 to x / 100.0 to get them both to behave the same.

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