Dans Mysql, il existe une astuce bon marché pour le faire :
mysql> select ~0;
+----------------------+
| ~0 |
+----------------------+
| 18446744073709551615 |
+----------------------+
le tilde est la négation au niveau du bit. La valeur résultante est un bigint. Voir :http://dev.mysql .com/doc/refman/5.1/en/bit-functions.html#operator_bitwise-invert
Pour les autres types d'entiers, vous pouvez utiliser le bon opérateur de décalage de bits >> comme ça :
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)
