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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;