In this post, I am sharing one user define function to generate Fibonacci Series in PostgreSQL.

Today Morning, I have started to take the interview for PostgreSQL Database Developer.

Generally, I am asking complex SQL Query, but this time I have asked to implement few mathematical logics like: “Write a small function to generate Fibonacci Series”.
Fibonacci Series means a series of numbers in which each number is the sum of the two preceding numbers.
e.g 1, 1, 2, 3, 5, 8, 13…

I am sharing this solution here, Database Developer should prepare yourself because Interviewer like, me can ask this kind of question.

Fibonacci Series Function:

CREATE OR REPLACE FUNCTION fn_Fibonacci(FNum INTEGER) 
RETURNS SETOF INTEGER
LANGUAGE SQL
AS $dbrnd$
WITH RECURSIVE cte(Num1,Num2) AS 
(
	VALUES(0,1)
	UNION ALL
        SELECT 
		GREATEST(Num1,Num2),Num1 + Num2 AS FibonacciSeries 
	FROM cte
        WHERE Num2 < FNum
)
SELECT Num1 FROM cte;
$dbrnd$;

Execute Function to generate Fibonacci Series upto 50:

SELECT *FROM fn_Fibonacci(50);

 fn_fibonacci
--------------
            0
            1
            1
            2
            3
            5
            8
           13
           21
           34
(10 rows)