PostgreSQL – Random Number Generation

When working with databases, there are times when you might need to generate random numbers for various use cases such as sampling data, testing, or creating unique values. PostgreSQL offers the built-in random() function, which returns a random number between 0 and 1. However, you can go beyond that by generating random numbers within a specific range or even creating a user-defined function (UDF) for more flexibility. This article will look into how to achieve this and provide practical examples.

PostgreSQL random() Function

The random() function in PostgreSQL generates a random floating-point number between 0 (inclusive) and 1 (exclusive). This can be particularly useful in a variety of scenarios.

Syntax:

Here’s the basic syntax:

SELECT random();

If you try the above syntax it will lead to the following:

Generating Random Numbers Within a Range

To generate a random number between 1 and 10, you use the following statement:

SELECT random() * 10 + 1 AS RAND_1_10;

If you try the above syntax it will lead to the following:

If you want to generate the random number as an integer, you apply the floor() function to the expression as follows:

SELECT floor(random() * 10 + 1)::int;

The above query results in the following:

The result will be an integer between 1 and 10.

Generating Random Numbers Between Two Custom Integers

Generally, to generate a random number between two integers l and h, you use the following statement:

SELECT floor(random() * (h-l+1) + l)::int;

For example, to generate a random number between 20 and 50:

SELECT floor(random() * (50 - 20 + 1) + 20)::int;

Creating a User-Defined Function for Random Numbers

To create a user-generated function that returns a random number between two numbers l and h:

CREATE OR REPLACE FUNCTION random_between(low INT ,high INT) 
   RETURNS INT AS
$$
BEGIN
   RETURN floor(random()* (high-low + 1) + low);
END;
$$ LANGUAGE 'plpgsql' STRICT;

The following statement calls the random_between() function and returns a random number between 1 and 100:

SELECT random_between(1,100);

Output:

The output will be an integer between 1 and 100.

Generating Multiple Random Numbers

If you want to get multiple random numbers between two integers, you use the following statement.

SELECT random_between(1,100)
FROM generate_series(1,5);

Output:

This statement returns five random integers within the specified range.