Syntax
LOG([B,]X)
Purpose
LOG(X) returns the natural logarithm of X, which is the base-e logarithm of X. If X is less than or equal to 0, the function returns NULL and reports the alert Invalid argument for logarithm. If only X is provided, this function is equivalent to LN(X).
You can call LOG(B,X) to return the logarithm of X to base B. If X is less than or equal to 0, or B is less than or equal to 1, the function returns NULL.
Examples
obclient> SELECT LOG(-10), LOG(0), LOG(10), LOG(-3.14), LOG(3.14);
+----------+--------+-------------------+------------+-------------------+
| LOG(-10) | LOG(0) | LOG(10) | LOG(-3.14) | LOG(3.14) |
+----------+--------+-------------------+------------+-------------------+
| NULL | NULL | 2.302585092994046 | NULL | 1.144222799920162 |
+----------+--------+-------------------+------------+-------------------+
1 row in set, 3 warnings
obclient> SELECT LOG(10, 100), LOG(1,100);
+--------------+------------+
| LOG(10, 100) | LOG(1,100) |
+--------------+------------+
| 2 | NULL |
+--------------+------------+
1 row in set, 1 warning