Syntax:
LOG10(X)
Returns the base-10 logarithm of X. If X is less than or equal to
0.0E0, the function returns NULL and a warning "Invalid argument for
logarithm" is reported.
mysql> SELECT LOG10(2);
-> 0.30102999566398
mysql> SELECT LOG10(100);
-> 2
mysql> SELECT LOG10(-100);
-> NULL
