MySQL CONV() 函数中的基数有下限和上限吗？如果 CONV() 函数中提供的基数超出限制会发生什么？

mysql> Select CONV(10,10,38);

+----------------+
| CONV(10,10,38) |
+----------------+
| NULL           |
+----------------+

1 row in set (0.00 sec)

mysql> Select CONV(10,7两,两);

+---------------+
| CONV(10,7两,两) |
+---------------+
| NULL          |
+---------------+

1 row in set (0.00 sec)

mysql> Select CONV(10,10,1);

+---------------+
| CONV(10,10,1) |
+---------------+
| NULL          |
+---------------+

1 row in set (0.00 sec)