Проблема совокупности MySQL

в следующем примере, почему мин () результаты возврата запроса, но Max ) Запрос не работает?

mysql> create table t(id int, a int);
Query OK, 0 rows affected (0.10 sec)

mysql> insert into t(id, a) values(1, 1);
Query OK, 1 row affected (0.03 sec)

mysql> insert into t(id, a) values(1, 2);
Query OK, 1 row affected (0.02 sec)

mysql> select * from t
    -> ;
+------+------+
| id   | a    |
+------+------+
|    1 |    1 |
|    1 |    2 |
+------+------+
2 rows in set (0.00 sec)

mysql> select * from t where a < 4;
+------+------+
| id   | a    |
+------+------+
|    1 |    1 |
|    1 |    2 |
+------+------+
2 rows in set (0.00 sec)

mysql> select * from t where a < 4 having a = max(a);
Empty set (0.00 sec)

mysql> select * from t where a < 4 having a = min(a);
+------+------+
| id   | a    |
+------+------+
|    1 |    1 |
+------+------+
1 row in set (0.00 sec)