How LOG2() Works in MariaDB

In MariaDB, LOG2() is a built-in function that returns the base-2 logarithm of its argument.

Syntax

The syntax goes like this:

LOG2(X)

Where X is the value for which to return the base-2 logarithm.

Example

Here’s an example to demonstrate:

SELECT LOG2(3);

Result:

+--------------------+
| LOG2(3)            |
+--------------------+
| 1.5849625007211563 |
+--------------------+

Here are some more:

SELECT 
    LOG2(2),
    LOG2(4),
    LOG2(8),
    LOG2(16);

Result:

+---------+---------+---------+----------+
| LOG2(2) | LOG2(4) | LOG2(8) | LOG2(16) |
+---------+---------+---------+----------+
|       1 |       2 |       3 |        4 |
+---------+---------+---------+----------+

Argument Ranges

If X is less than or equal to 0, then NULL is returned with a warning.

SELECT 
    LOG2(0),
    LOG2(-1);

Result:

+---------+----------+
| LOG2(0) | LOG2(-1) |
+---------+----------+
|    NULL |     NULL |
+---------+----------+
1 row in set, 2 warnings (0.000 sec)

Let’s check the warnings:

SHOW WARNINGS;

Result:

+---------+------+---------------+
| Level   | Code | Message       |
+---------+------+---------------+
| Warning | 1365 | Division by 0 |
| Warning | 1365 | Division by 0 |
+---------+------+---------------+

Non-Numeric Arguments

Here’s an example of what happens when we provide non-numeric arguments:

SELECT LOG2('Dog');

Result:

+-------------+
| LOG2('Dog') |
+-------------+
|        NULL |
+-------------+
1 row in set, 2 warnings (0.000 sec)

Let’s see the warning:

SHOW WARNINGS;

Result:

+---------+------+-----------------------------------------+
| Level   | Code | Message                                 |
+---------+------+-----------------------------------------+
| Warning | 1292 | Truncated incorrect DOUBLE value: 'Dog' |
| Warning | 1365 | Division by 0                           |
+---------+------+-----------------------------------------+

Null Arguments

LOG2() returns null if its argument is null:

SELECT LOG2(null);

Result:

+------------+
| LOG2(null) |
+------------+
|       NULL |
+------------+

Missing Arguments

Calling LOG2() with the wrong number of arguments, or without any arguments results in an error:

SELECT LOG2();

Result:

ERROR 1582 (42000): Incorrect parameter count in the call to native function 'LOG2'

And:

SELECT LOG2(10, 2);

Result:

ERROR 1582 (42000): Incorrect parameter count in the call to native function 'LOG2'