[HackerRank] Symmetric Pairs

 

 

[문제]

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[MySQL]

SELECT F1.X
     , F1.Y
FROM Functions AS F1
    INNER JOIN Functions AS F2 ON F1.X = F2.Y AND F1.Y = F2.X
GROUP BY F1.X, F1.Y
HAVING F1.X < F1.Y 
    OR COUNT(F1.X) >= 2
ORDER BY F1.X ASC