更新时间:2022-12-12 14:28:56
在Mysql中,有一个便宜的技巧可以做到这一点:
In Mysql there is a cheap trick to do this:
mysql> select ~0;
+----------------------+
| ~0 |
+----------------------+
| 18446744073709551615 |
+----------------------+
波浪号是按位取反.结果值是bigint.请参阅: http://dev.mysql.com /doc/refman/5.1/en/bit-functions.html#operator_bitwise-invert
the tilde is the bitwise negation. The resulting value is a bigint. See: http://dev.mysql.com/doc/refman/5.1/en/bit-functions.html#operator_bitwise-invert
对于其他整数口味,您可以像这样使用正确的位移运算符>>
:
For the other integer flavours, you can use the right bitshift operator >>
like so:
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)