我试图从MysqL数据库中找出一个整数(有符号或无符号)的最大值.有没有办法从数据库本身拉回这些信息？
是否有任何内置的常量或函数我可以使用(标准sql或MysqL具体).
在http://dev.mysql.com/doc/refman/5.0/en/numeric-types.html它列出了值 – 但是有一种数据库告诉我的方法.
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
提前致谢,
解决方法
在MysqL中有一个很便宜的手段：
MysqL> select ~0; +----------------------+ | ~0 | +----------------------+ | 18446744073709551615 | +----------------------+
波浪号是逐位否定.得到的值是一个bigint.见：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操作符>>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)
