Confused on this one.
Same version of MySQL running on both servers. (built from exact same rpm's) - somewhere along the line some developer changed something...
Server 1:
mysql> select ( not 1 = 2 );
0
1 row in set (0.00 sec)
Server 2:
mysql> select ( not 1 = 2 );
1
1 row in set (0.00 sec)
Both servers:
mysql> sHOW VARIABLES LIKE 'version';
| version | 5.6.12 |
You should check the HIGH_NOT_PRECEDENCE operator.
The official documentation states:
The precedence of the NOT operator is such that expressions such as NOT a BETWEEN b AND c are parsed as NOT (a BETWEEN b AND c). In some older versions of MySQL, the expression was parsed as (NOT a) BETWEEN b AND c. The old higher-precedence behavior can be obtained by enabling the HIGH_NOT_PRECEDENCE SQL mode.
Fiddle to test this behaviour here.
By the way, I would recommend to compare x != y rather than using not (x = y).