PostgreSQL random function.

Preamble

PostgreSQL random function can be used to return a random number or a random number within a range.

Syntax of the random PostgreSQL function

random( )

Parameters and function arguments

• There are no parameters or arguments for the random function.

Note:

• The random function will return a value from 0 (inclusive) to 1 (excluding), so the value will be in the range >= 0 and <1.
• Use the set seed function to set the initial value for random.
• The random function returns a completely random number if no initial number is set (the initial value is set by the set seed function).
• The random function will return a repeatable sequence of random numbers every time a specific initial value is used (the initial value is set using the set seed function).

Random decimal range

To create a random decimal number between two values (range), you can use the following formula:

SELECT random()*(b-a)+a;

Where a is the smallest number, and b is the largest number for which you want to generate a random number.

SELECT random()*(25-10)+10;

The above formula will generate a random decimal number >= 10 and < 25. (Note: this formula will never return 25 because random will never return 1).

Random range of integers

To create a random integer between two values (range), you can use the following formula:

SELECT floor(random()*(b-a+1))+a;

Where a is the smallest number, and b is the largest number for which you want to generate a random number.

SELECT floor(random()*(25-10+1))+10;

The above formula will generate a random integer from 10 to 25 inclusive.

The random function can be used in the following PostgreSQL versions

PostgreSQL 11, PostgreSQL 10, PostgreSQL 9.6, PostgreSQL 9.5, PostgreSQL 9.4, PostgreSQL 9.3, PostgreSQL 9.2, PostgreSQL 9.1, PostgreSQL 9.0, PostgreSQL 8.4.

Example of a random number

Let’s see how to use the random function in PostgreSQL to generate a random number >= 0 and < 1. For example:

SELECT random();

-Result: 0.0186054138466716

Although the random function will return a value above 0, it will never return a value of 1. It will always return a value below 1.

Example of a random decimal range

Let’s see how to use the PostgreSQL random function to generate a random decimal number between two numbers (i.e.: range).
For example, the next one will generate a random decimal value that >= 1 and < 10 (Note: it will never return 10):

SELECT random()*(10-1)+1;

--Result: 1.40731927193701

In the following example, a random decimal value >= 25 and < 40 will be generated (Note: it will never return 40):

SELECT random()*(40-25)+25;

--Result: 33.7993366038427

Example of a random integer range

Let’s see how to use the random function in PostgreSQL to generate a random integer between two numbers (i.e.: including the range).
For example, the next one will generate a random integer value from 1 to 10:

SELECT floor(random()*(10-1+1))+1;

--Result: 6

In the following example, a random integer value between 25 and 40 will be generated:

SELECT floor(random()*(40-25+1))+25;

--Result: 28

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