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Overview

The LOG() function returns the base-10 logarithm or logarithm of the specified base of a given number.

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Syntax

The following illustrates the syntax of the LOG() function:

-- base-10 logarithm
LOG(number)

-- logarithm of number
LOG(base, number)

Where:

• base: The base number. It must be greater than 0 and not equal to 1.

• number: The number whose logarithm you want to obtain. It must be a positive number and greater than 0.

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Examples

Let’s explore some examples of the LOG() function.

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Case #1: Get base-10 logarithm

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1. Basic Usage

In this case, the LOG() function calculates the base-10 logarithm of a specified number.

SELECT LOG(2), LOG(2.5);

You will get the output below:

        log         |   log   
--------------------+---------
 0.3010299956639812 | 0.39794

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2. Using Negative Value

In this example, the LOG() function is applied to negative numbers.

SELECT LOG(-1);

Any input of negative values will give you a NaN result.

 log 
-----
 NaN

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3. Using Null Value

The LOG() function will return NULL if the argument is NULL.

SELECT LOG(null);

You will get a null result when an argument passed is null.

 log 
-----
    

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4. Using Zero Value

In this example, the LOG() takes zero as an argument.

SELECT LOG(0);

You will get the output below:

    log    
-----------
 -Infinity

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Case #2: Get Logarithm

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1. Basic Usage

In this case, the LOG() function calculates the logarithm of a specified number.

SELECT LOG(4, 16), 
       LOG(0.7, 0.8), 
       LOG(0.5, 10),
       LOG(1, null);

You will get the output below:

 log |    log     |    log    | log 
-----+------------+-----------+-----
   2 | 0.62562156 | -3.321928 |    

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2. Using Table

Consider a database table called data with the following records:

CREATE TABLE data (
    data_column TEXT,
    x REAL,
    y REAL
);

INSERT INTO data (data_column, x, y) VALUES 
('Data 1', 0.5, 2),
('Data 2', 1, 2),
('Data 3', 5, 2),
('Data 4', 10, 10),
('Data 5', 50, 10);

SELECT * FROM data;

 data_column |  x  | y  
-------------+-----+----
 Data 1      | 0.5 |  2
 Data 2      |   1 |  2
 Data 3      |   5 |  2
 Data 4      |  10 | 10
 Data 5      |  50 | 10

Use the LOG() function to calculate the logarithm of column x (as a base) and column *y *(as a number):

SELECT *, LOG(y, x) AS LOG_Value FROM data;

You will get the result as shown below:

 data_column |  x  | y  | log_value 
-------------+-----+----+-----------
 Data 1      | 0.5 |  2 |        -1
 Data 2      |   1 |  2 |         0
 Data 3      |   5 |  2 |  2.321928
 Data 4      |  10 | 10 |         1
 Data 5      |  50 | 10 |   1.69897