Symmetric Pairs HackerRank SQL Solution in MYSQL

Problem:-

You are given a table, Functions, containing two columns: X and Y.

Two pairs (X1, Y1) and (X2, Y2) are said to be symmetric pairs if X1 = Y2 and X2 = Y1.

Write a query to output all such symmetric pairs in ascending order by the value of X.

Sample Input

Sample Output

20 20
20 21
22 23

Solution:-

select x, y from functions f1 
    where exists(select * from functions f2 where f2.y=f1.x 
    and f2.x=f1.y and f2.x>f1.x) and (x!=y) 
union 
select x, y from functions f1 where x=y and 
    ((select count(*) from functions where x=f1.x and y=f1.x)>1)    

        order by x;