In the last episode (Nov 18), Ahmad Al-Twaijiry said:
> I have a column in a table defined as float
>
> mynumber float(20,2)
>
> if we say mynumber column in a row is 1000000 , when I run this SQL :
>
> UPDATE Table SET mynumber=mynumber-100.15
>
> the mynumber column will be 999900 not 999899.85
>
> what is the problem ?
It works for me (approximately) in mysql 5.1:
mysql> create table blah ( mynumber float(20,2) );
mysql> insert into blah values ( 1000000 );
mysql> update blah SET mynumber=mynumber-100.15;
mysql> select * from blah;
+-----------+
| mynumber |
+-----------+
| 999899.88 |
+-----------+
1 row in set (0.02 sec)
Since base-10 fractions can't be represented exactly by a base-2
floating-point number, any fractional value you store will be
imprecisely stored and will cuase rounding errors. You probably want
to use the DECIMAL type instead of FLOAT.
http://dev.mysql.com/doc/refman/5.0/en/numeric-type-overview.html
--
Dan Nelson
dnelson@stripped
