LOG

14min
Overview
The  LOG() function returns the base-10 logarithm or logarithm of the specified base of a given number.
Syntax
The following illustrates the syntax of the LOG() function:
Pgsql
-- base-10 logarithm
LOG(number)

-- logarithm of number
LOG(base, number)
-- base-10 logarithm
LOG(number)

-- logarithm of number
LOG(base, number)
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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.
Examples
Let's explore some examples of the LOG() function.
Case #1: Get base-10 logarithm
1. Basic Usage
In this case, the LOG() function calculates the base-10 logarithm of a specified number.
Pgsql
SELECT LOG(2), LOG(2.5);
SELECT LOG(2), LOG(2.5);
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You will get the output below:
Pgsql
        log         |   log   
--------------------+---------
 0.3010299956639812 | 0.39794
        log         |   log   
--------------------+---------
 0.3010299956639812 | 0.39794
﻿
2. Using Negative Value
In this example, the LOG() function is applied to negative numbers.
Pgsql
SELECT LOG(-1);
SELECT LOG(-1);
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Any input of negative values will give you a NaN result.
Pgsql
 log 
-----
 NaN
 log 
-----
 NaN
﻿
3. Using Null Value
The LOG() function will return NULL if the argument is NULL.
Pgsql
SELECT LOG(null);
SELECT LOG(null);
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You will get a null result when an argument passed is null.
Pgsql
 log 
-----
    
 log 
-----
    
﻿
4. Using Zero Value
In this example, the LOG() takes zero as an argument.
Pgsql
SELECT LOG(0);
SELECT LOG(0);
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You will get the output below:
Pgsql
    log    
-----------
 -Infinity
    log    
-----------
 -Infinity
﻿
Case #2: Get Logarithm
1. Basic Usage
In this case, the LOG() function calculates the logarithm of a specified number.
Pgsql
SELECT LOG(4, 16), 
       LOG(0.7, 0.8), 
       LOG(0.5, 10),
       LOG(1, null);
SELECT LOG(4, 16), 
       LOG(0.7, 0.8), 
       LOG(0.5, 10),
       LOG(1, null);
﻿
You will get the output below:
Pgsql
 log |    log     |    log    | log 
-----+------------+-----------+-----
   2 | 0.62562156 | -3.321928 |    
 log |    log     |    log    | log 
-----+------------+-----------+-----
   2 | 0.62562156 | -3.321928 |    
﻿
2. Using Table
Consider a database table called data with the following records:
Pgsql
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;
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;
﻿
Pgsql
 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
 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):
Pgsql
SELECT *, LOG(y, x) AS LOG_Value FROM data;
SELECT *, LOG(y, x) AS LOG_Value FROM data;
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You will get the result as shown below:
Pgsql
 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
 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
﻿
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