expr NOT BETWEEN min AND max is the same as NOT (expr BETWEEN min AND max).
If expr is greater than or equal to min and expr is less than or equal to max, BETWEEN returns 1.
Otherwise it returns 0.
This is equivalent to the expression (min
mysql>
mysql> SELECT 1 BETWEEN 2 AND 3;
+-------------------+
| 1 BETWEEN 2 AND 3 |
+-------------------+
| 0 |
+-------------------+
1 row in set (0.00 sec)
mysql>