A few days ago I needed to get max unsigned big int in MySQL. Here is a little trick on how to get it right away:

mysql> SELECT ~0;
+----------------------+
| ~0                   |
+----------------------+
| 18446744073709551615 |
+----------------------+
1 row in set (0.01 sec)

So, what is ~ ? It calls bitwise inversion.

But what if I want max signed big int? Here you are:

mysql> SELECT ~0 >> 1;
+---------------------+
| ~0 >> 1             |
+---------------------+
| 9223372036854775807 |
+---------------------+
1 row in set (0.00 sec)

Ok... Let's try something else :)

Ok, I want to have a max unsigned int and signed. It should be >> 32 for unsigned and >> 33 for the signed one. Let's try

mysql> SELECT ~0 >> 32 as 'unsigned',
    -> ~0 >> 33 as 'signed';
+------------+------------+
| unsigned   | signed     |
+------------+------------+
| 4294967295 | 2147483647 |
+------------+------------+
1 row in set (0.01 sec)

Hope someone will find it useful :)