LOG(X), LOG(B,X): If called with one parameter, this function returns the natural logarithm of X : LOG « Math Numeric Functions « MySQL Tutorial

1. MySQL Tutorial
2. Math Numeric Functions
3. LOG

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

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

mysql>