Symmetric Pairs in SQL | HackerRank Programming Solutions | HackerRank SQL Solutions

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Introduction To SQL

SQL stands for Structured Query Language. SQL is used to create, remove, alter the database and database objects in a database management system and to store, retrieve, update the data in a database. SQL is a standard language for creating, accessing, manipulating database management system. SQL works for all modern relational database management systems, like SQL Server, Oracle, MySQL, etc.

• It is a standard language for Relational Database System. It enables a user to create, read, update and delete relational databases and tables.
• All the RDBMS like MySQL, Informix, Oracle, MS Access and SQL Server use SQL as their standard database language.
• SQL allows users to query the database in a number of ways, using English-like statements.

Link for the Problem – Symmetric Pairs SQl – Hacker Rank Solution

Symmetric Pairs SQl – Hacker Rank Solution

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. List the rows such that X₁ ≤ Y₁.

Sample Input2

Sample Output

20 20
20 21
22 23

Symmetric Pairs SQl – Hacker Rank 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;