NOT, !
Logical NOT. Evaluates to 1 if the operand is 0, to 0 if the operand is non-zero, and NOT NULL returns NULL.

mysql> SELECT * FROM test;
+----+----------+
| id | num      |
+----+----------+
|  1 |      148 |
|  2 | 68767867 |
+----+----------+
2 rows in set (0.00 sec)

mysql> SELECT * FROM test WHERE NOT(id)=null;
Empty set (0.00 sec)

mysql> SELECT * FROM test WHERE !(id)=null;
Empty set (0.00 sec)

mysql> SELECT * FROM test WHERE NOT(id)=false;
+----+----------+
| id | num      |
+----+----------+
|  1 |      148 |
|  2 | 68767867 |
+----+----------+
2 rows in set (0.00 sec)

mysql> SELECT * FROM test WHERE !(id)=false;
+----+----------+
| id | num      |
+----+----------+
|  1 |      148 |
|  2 | 68767867 |
+----+----------+
2 rows in set (0.00 sec)

mysql> SELECT * FROM test WHERE NOT(id)=true;
+----+----------+
| id | num      |
+----+----------+
|  2 | 68767867 |
+----+----------+
1 row in set (0.00 sec)

mysql> SELECT * FROM test WHERE !(id)=true
Empty set (0.00 sec)