我试图从 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提取这些信息？
是否有我可以使用的内置常量或函数（标准 SQL 或 MySQL 特定的）。
At http://dev.mysql.com/doc/refman/5.0/en/numeric-types.html http://dev.mysql.com/doc/refman/5.0/en/numeric-types.html它列出了值 - 但数据库有没有办法告诉我。
以下给出了 MAX_BIGINT - 我想要的是 MAX_INT。
SELECT CAST( 99999999999999999999999 AS SIGNED ) as max_int;
# max_int | 9223372036854775807
在 Mysql 中，有一个廉价的技巧可以做到这一点：
mysql> select ~0;
+----------------------+
| ~0 |
+----------------------+
| 18446744073709551615 |
+----------------------+
波形符是按位求反。结果值是一个 bigint。看：http://dev.mysql.com/doc/refman/5.1/en/bit-functions.html#operator_bitwise-invert http://dev.mysql.com/doc/refman/5.1/en/bit-functions.html#operator_bitwise-invert
对于其他整数风格，您可以使用正确的位移运算符>>像这样：
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)
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