From: Alex Keda
Date: February 15 2013 11:07am
Subject: Re: MySQL 5.1: incorrect arithmetic calculation
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15.02.2013 14:43, Johan De Meersman пишет:
>
> ----- Original Message -----
>> From: "Alex Keda" <admin@stripped>
>>
>> mysql> SELECT SUM(`Amount`*`Cost`*(1-`Discont`)) as `Summ` FROM `WorksCompliteAgregate` WHERE (`ContractID` = 10369 AND `Month` = 497);
> Based off the select you printed, this comes to EXACTLY 548.595 for the first row and 0 for the second row.
>
>
>> mysql> SELECT SUM(`Amount`*`Cost`*(1-`Discont`)*100)/100 as `Summ` FROM `WorksCompliteAgregate` WHERE (`ContractID` = 10369 AND `Month` = 497);
> The more detailed result here, though, seems to suggest that there's a longer fraction in your table than is printed by your select. Would your column happen to be a Float?
>
>> but, my desktop calculator gives the result 548.60
> Which is the correct rounding for 548.595. Check if your column is a float, and if it is, go google for floating point mathematics. They do not work the way you think they do. Use decimal(n,m) for money - or any discrete number, for that matter. Floats are not exact values, they are APPROXIMATE values.
>
> https://dev.mysql.com/doc/refman/5.0/en/problems-with-float.html may also give you an idea of what goes wrong.
>
>
OK. But, how about:
mysql> SELECT 365 * 1.67 * ( 1 - 0.10);
+--------------------------+
| 365 * 1.67 * ( 1 - 0.10) |
+--------------------------+
|                 548.5950 |
+--------------------------+
1 row in set (0.00 sec)

mysql>
??