PostgreSQL LN() Function

Summary: in this tutorial, you will learn how to use the PostgreSQL LN() function to calculate the natural logarithm of a number.

Introduction to the PostgreSQL LN() function

The natural logarithm is a function that represents the logarithm to base e, where e is Euler’s number, which is approximately equal to 2.71828.

In Math, the natural logarithm of a x is denoted as ln(x).

If ln(x) = y, then e^y = x.

In PostgreSQL, you use the LN() function to calculate the natural logarithm of a number.

Here’s the syntax of the LN() function:

LN(n)Code language: SQL (Structured Query Language) (sql)

In this syntax:

• n is a number with the type numeric or double precision. It can be a literal number, an expression, or a table column. n cannot be zero.

The LN() function returns the natural logarithm of n with the type corresponding to the type of n. It returns NULL if n is NULL.

If n is a string, the LN() function will convert it to a type numeric or double precision value. If the conversion fails, the LN() function raises an error.

The LN() function is the inverse of the EXP() function that returns the exponential value of a number.

PostgreSQL LN() function examples

Let’s take some examples of using the LN() function.

1) Basic PostgreSQL LN() function examples

The following example uses the LN() function to return the natural logarithm of 10:

SELECT LN(10) result;Code language: SQL (Structured Query Language) (sql)

Output:

      result
-------------------
 2.302585092994046Code language: SQL (Structured Query Language) (sql)

The following statement uses the LN() function to return the natural logarithm of e:

SELECT LN(EXP(1)) result;Code language: SQL (Structured Query Language) (sql)

Output:

 result
--------
      1Code language: SQL (Structured Query Language) (sql)

In this example, the EXP(1) function returns e¹, which is e. Then, the LN() function returns the natural logarithm of e, which returns 1.

2) Using the LN() function with text

The following example uses the LN() function to calculate the natural logarithm of a numeric string ’10’

SELECT LN('10') result;Code language: SQL (Structured Query Language) (sql)

Output:

      result
-------------------
 2.302585092994046Code language: SQL (Structured Query Language) (sql)

In this example, the LN() function converts the string ’10’ to a number before calculating the natural logarithm.

The following example attempts to calculate the natural logarithm of the string ’10x’:

SELECT LN('10x') result;Code language: SQL (Structured Query Language) (sql)

The function raises an error because it cannot convert the string ’10x’ to a number:

ERROR:  invalid input syntax for type double precision: "10x"
LINE 1: SELECT LN('10x') result;
                  ^Code language: SQL (Structured Query Language) (sql)

Summary

• Use the LN() function to calculate the natural logarithm of a number.