mysql>
mysql> SELECT LN(2);
+------------------+
| LN(2) |
+------------------+
| 0.69314718055995 |
+------------------+
1 row in set (0.00 sec)
mysql>
mysql> SELECT LN(-2);
+--------+
| LN(-2) |
+--------+
| NULL |
+--------+
1 row in set (0.00 sec)
mysql>