HackerRank MySQL - 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.
- 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;
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