| Oracle® Database SQL Reference 10g Release 2 (10.2) Part Number B14200-02  | 
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Syntax

Purpose
LN returns the natural logarithm of n, where n is greater than 0.
This function takes as an argument any numeric datatype or any nonnumeric datatype that can be implicitly converted to a numeric datatype. If the argument is BINARY_FLOAT, then the function returns BINARY_DOUBLE. Otherwise the function returns the same numeric datatype as the argument.
Examples
The following example returns the natural logarithm of 95:
SELECT LN(95) "Natural log of 95" FROM DUAL;
Natural log of 95
-----------------
       4.55387689