pbm with SUM

When I do:

mysql> select montant from virement_ordres;
+---------+
| montant |
+---------+
| 1234.4 |
| 0.5 |
+---------+
2 rows in set (0.00 sec)

mysql> select sum(montant) from virement_ordres;
+-----------------+
| sum(montant) |
+-----------------+
| 1234.9000244141 |
+-----------------+
1 row in set (0.00 sec)

Is the error of rounding normal ?

For information, I'm using:
Server version: 4.0.13-log
The server is running under linux.

And "montant" is a float.

Best regards,
Edouard.

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Re: pbm with SUM

Edouard,

Edouard Vanbelle wrote:
> When I do:
>
> mysql> select montant from virement_ordres;
> +---------+
> | montant |
> +---------+
> | 1234.4 |
> | 0.5 |
> +---------+
> 2 rows in set (0.00 sec)
>
> mysql> select sum(montant) from virement_ordres;
> +-----------------+
> | sum(montant) |
> +-----------------+
> | 1234.9000244141 |
> +-----------------+
> 1 row in set (0.00 sec)
>
> Is the error of rounding normal ?

Yes it is normal. See below




> And "montant" is a float.

This is the reason. Rounding errors are normal with floats.

When dealing with float values MySQL users floating point arithmetic which is
never precise in computers world. Or in other words it is precise up to some digit
after decimal point.

See more examples.

create table f (f float);
insert into f values (1234.4), (0.5);

mysql> select f, f+0, round(f, 20) from f;
+--------+-----------------+---------------------------+
| f | f+0 | round(f, 20) |
+--------+-----------------+---------------------------+
| 1234.4 | 1234.4000244141 | 1234.40002441406250000000 |
| 0.5 | 0.5 | 0.50000000000000000000 |
+--------+-----------------+---------------------------+


See also MySQL manual:

http://www.mysql.com/doc/en/Problems_with_float.html




> Best regards,
> Edouard.
>
> --
> OVH
> 140 Quai du Sartel
> 59100 Roubaix
> France

Best regards



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