[HackerRank MySQL] Symmetric Pairs

Symmetric Pairs

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. List the rows such that X1 ≤ Y1.

 

Sample Input

Sample Output

20 20
20 21
22 23

 

Query

select f1.x, f1.y
from functions f1 inner join functions f2
on f1.x = f2.y and f2.x = f1.y
group by f1.x, f1.y
having count(*) >= 2 or f1.x < f1.y
order by 1

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Reference: HackerRank Practice > SQL > Advanced Join > Symmetric Pairs