Bug #43262 Float values lose precision when dumped out and reloaded

• Submitted: 27 Feb 2009 13:26
• Modified: 27 Feb 2009 15:50
• Reporter: Balint Toth
• Status: Not a Bug
• Category: MySQL Server: Data Types
• Severity: S3 (Non-critical)
• Version: 5.0.30, 5.1.31
• OS: Linux
• CPU Architecture: Any
• Tags: float dump

[27 Feb 2009 13:26] Balint Toth

Description:
When you dump a table with float values precision is lost.

Also when you just select the previously inserted row, it's rounded.

How to repeat:
CREATE TABLE `ftest` (
  `f` float default NULL
) ENGINE=MyISAM DEFAULT CHARSET=latin1;

insert into ftest values (10000.78);

mysql> select * from ftest;
+---------+
| f       |
+---------+
| 10000.8 | 
+---------+

mysql> select f*100 from ftest;
+-----------------+
| f*100           |
+-----------------+
| 1000078.0273438 | 
+-----------------+

mysqldump output:
INSERT INTO `ftest` VALUES (10000.8);

When you convert the field to a decimal type, the decimals appear:

mysql> alter table ftest modify f decimal(12,4);
Query OK, 1 row affected, 1 warning (0.03 sec)
Records: 1  Duplicates: 0  Warnings: 1

mysql> select * From ftest;
+------------+
| f          |
+------------+
| 10000.7803 | 
+------------+
1 row in set (0.00 sec)

[27 Feb 2009 15:50] Valeriy Kravchuk

Thank you for taking the time to write to us, but this is not a bug. Please double-check the documentation available at http://dev.mysql.com/doc/refman/5.1/en/problems-with-float.html and the instructions on how to report a bug at http://bugs.mysql.com/how-to-report.php