我正在尝试从MySQL数据库中找出整数（有符号或无符号）的最大值。有没有办法从数据库本身撤回此信息？
有没有我可以使用的内置常量或函数（标准SQL或MySQL专用）。
在http://dev.mysql.com/doc/refman/5.0/en/numeric- types.html上，它列出了值- 但是数据库有一种方法可以告诉我。
以下是MAX_BIGINT-我想要的是MAX_INT。
SELECT CAST( 99999999999999999999999 AS SIGNED ) as max_int; # max_int | 9223372036854775807
在Mysql中，有一个便宜的技巧可以做到这一点：
mysql> select ~0; +----------------------+ | ~0 | +----------------------+ | 18446744073709551615 | +----------------------+
波浪号是按位取反。结果值是bigint。参见：http : //dev.mysql.com/doc/refman/5.1/en/bit-functions.html#operator_bitwise- invert
对于其他整数型，可以使用正确的bitshift运算符，>>如下所示：
>>
SELECT ~0 as max_bigint_unsigned , ~0 >> 32 as max_int_unsigned , ~0 >> 40 as max_mediumint_unsigned , ~0 >> 48 as max_smallint_unsigned , ~0 >> 56 as max_tinyint_unsigned , ~0 >> 1 as max_bigint_signed , ~0 >> 33 as max_int_signed , ~0 >> 41 as max_mediumint_signed , ~0 >> 49 as max_smallint_signed , ~0 >> 57 as max_tinyint_signed \G *************************** 1. row *************************** max_bigint_unsigned: 18446744073709551615 max_int_unsigned: 4294967295 max_mediumint_unsigned: 16777215 max_smallint_unsigned: 65535 max_tinyint_unsigned: 255 max_bigint_signed: 9223372036854775807 max_int_signed: 2147483647 max_mediumint_signed: 8388607 max_smallint_signed: 32767 max_tinyint_signed: 127 1 row in set (0.00 sec)
