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HomeDatabaseMysql TutorialMySQL整型数据溢出的处理策略_MySQL

作者:吴炳锡 来源:http://www.mysqlsupport.cn/ 联系方式: wubingxi#gmail.com 转载请注明作/译者和出处,并且不能用于商业用途,违者必究.

今天接到一个朋友电话说是觉的数据库被别人更改了,出现数据不对的问题 。经过很久的排查是数据类型溢出了(发生问题的版本是MySQL 5.1)。后来通过给朋友那边把MySQL 5.1升级到MySQL 5.5去解决这个问题。 这也让我有兴趣去了解一下MySQL不同版本数据类型溢出的处理机制。

先看一下MySQL支持的整型数及大小,存储空间:

Type Storage Minimum Value Maximum Value 存储大小
(Bytes) (Signed/Unsigned) (Signed/Unsigned) byte
TINYINT 1 -128 127 1 byte
0 255
SMALLINT 2 -32768 32767 2 bytes
0 65535
MEDIUMINT 3 -8388608 8388607 3 bytes
0 16777215
INT 4 -2147483648 2147483647 4 bytes
0 4294967295
BIGINT 8 -9223372036854775808 9223372036854775807 8 bytes
0 18446744073709551615

另外请记着mysql的数据处理会转成bigint处理,所以这里就用bigint几个测试:

SELECT CAST(0 AS UNSIGNED) - 1; SELECT 9223372036854775807 + 1;

MySQL 5.1 下:

mysql> SELECT CAST(0 AS UNSIGNED) - 1;+-------------------------+| CAST(0 AS UNSIGNED) - 1 |+-------------------------+|18446744073709551615 |+-------------------------+1 ROW IN SET (0.01 sec) mysql> SELECT 9223372036854775807 + 1;+-------------------------+| 9223372036854775807 + 1 |+-------------------------+|-9223372036854775808 |+-------------------------+1 ROW IN SET (0.01 sec)

MySQL 5.5, 5.6, 5.7下:

mysql> SELECT CAST(0 AS UNSIGNED) - 1;ERROR 1690 (22003): BIGINT UNSIGNED VALUE IS OUT OF range IN '(cast(0 as unsigned) - 1)'mysql> mysql> mysql> mysql> SELECT 9223372036854775807 + 1;ERROR 1690 (22003): BIGINT VALUE IS OUT OF range IN '(9223372036854775807 + 1)'

所在处理这类数据是一定要小心溢出(如早期有做弊冲Q币就是利用这个方法处理)

这个问题有可能会出现积分消息,积分相加, 或是一些钱相关的业务中出现, 主库5.1 ,从库MySQL 5.5情况也会出现不同步的问题。
建议:这类业务系统尽可能的升级到MySQL 5.5后版本

更多详情参考: http://dev.mysql.com/doc/refman/5.7/en/out-of-range-and-overflow.html

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