MySQL Bugs: #72056: Wrong comparsion on big DECIMAL values

Bug #72056	Wrong comparsion on big DECIMAL values
Submitted:	17 Mar 2014 10:19	Modified:	21 May 2015 0:51
Reporter:	Artem Zaytsev	Email Updates:
Status:	Closed	Impact on me:	None
Category:	MySQL Server: DML	Severity:	S1 (Critical)
Version:	5.5/5.6	OS:	Linux
Assigned to:	Tor Didriksen	CPU Architecture:	Any
Tags:	decimal

Description:
Comparison works differently for the search by index and without index

How to repeat:
mysql> CREATE TABLE `decimalTest`(`value` DECIMAL(24,0) NOT NULL);
Query OK, 0 rows affected (0.01 sec)

mysql> INSERT INTO `decimalTest`(`value`) VALUES('100000000000000000000001'), ('100000000000000000000002'), ('100000000000000000000003');
Query OK, 3 rows affected (0.00 sec)
Records: 3  Duplicates: 0  Warnings: 0

mysql> SELECT * FROM `decimalTest` WHERE `value` = '100000000000000000000002';
+--------------------------+
| value                    |
+--------------------------+
| 100000000000000000000001 |
| 100000000000000000000002 |
| 100000000000000000000003 |
+--------------------------+
3 rows in set (0.00 sec)

mysql> SELECT * FROM `decimalTest` WHERE `value` = 100000000000000000000002;
+--------------------------+
| value                    |
+--------------------------+
| 100000000000000000000002 |
+--------------------------+
1 row in set (0.00 sec)

mysql> ALTER TABLE `decimalTest` ADD INDEX `value` (`value`);
Query OK, 0 rows affected (0.01 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql> SELECT * FROM `decimalTest` WHERE `value` = '100000000000000000000002';
+--------------------------+
| value                    |
+--------------------------+
| 100000000000000000000002 |
+--------------------------+
1 row in set (0.00 sec)

mysql> SELECT * FROM `decimalTest` WHERE `value` = 100000000000000000000002;
+--------------------------+
| value                    |
+--------------------------+
| 100000000000000000000002 |
+--------------------------+
1 row in set (0.00 sec)

mysql>

Thank you for the bug report.

C:\dbs>c:\dbs\5.6\bin\mysql -uroot --port=3560 --prompt="mysql 5.6 > "
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 1
Server version: 5.6.17 Source distribution

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affiliates. Other names may be trademarks of their respective
owners.

Type 'help;' or '\h' for help. Type '\c' to clear the current input statement.

mysql 5.6 > use test
Database changed
mysql 5.6 > CREATE TABLE `decimalTest`(`value` DECIMAL(24,0) NOT NULL);
Query OK, 0 rows affected (0.42 sec)

mysql 5.6 >  INSERT INTO `decimalTest`(`value`) VALUES('100000000000000000000001'), ('100000000000000000000002'), ('100000000000000000000003');
Query OK, 3 rows affected (0.09 sec)
Records: 3  Duplicates: 0  Warnings: 0

mysql 5.6 > SELECT * FROM `decimalTest` WHERE `value` = '100000000000000000000002';
+--------------------------+
| value                    |
+--------------------------+
| 100000000000000000000001 |
| 100000000000000000000002 |
| 100000000000000000000003 |
+--------------------------+
3 rows in set (0.06 sec)

mysql 5.6 > SELECT * FROM `decimalTest` WHERE `value` = 100000000000000000000002;
+--------------------------+
| value                    |
+--------------------------+
| 100000000000000000000002 |
+--------------------------+
1 row in set (0.03 sec)

mysql 5.6 > ALTER TABLE `decimalTest` ADD INDEX `value` (`value`);
Query OK, 0 rows affected (0.37 sec)
Records: 0  Duplicates: 0  Warnings: 0

mysql 5.6 > SELECT * FROM `decimalTest` WHERE `value` = '100000000000000000000002';
+--------------------------+
| value                    |
+--------------------------+
| 100000000000000000000002 |
+--------------------------+
1 row in set (0.02 sec)

mysql 5.6 > SELECT * FROM `decimalTest` WHERE `value` = 100000000000000000000002;
+--------------------------+
| value                    |
+--------------------------+
| 100000000000000000000002 |
+--------------------------+
1 row in set (0.00 sec)

mysql 5.6 >

Unfortunately, this result is according to our documentation:
http://dev.mysql.com/doc/refman/5.6/en/type-conversion.html
"In all other cases, the arguments are compared as floating-point (real) numbers."

The quoted literal is treated as a string, and 100000000000000000000002
has more than DBL_DIG == 15 digits, so floating-point comparison treats
them as equal.

Noted in 5.7.8, 5.8.0 changelogs.

Large integer literals converted to floats for comparison with
decimal data could lose precision and produce incorrect results.