HackerRank: [SQL Advanced Select] (1/5) TYPE OF TRIANGLE | case when in SQL

I started studying SQL from a very famous site - HackerRank. Here I will try to provide multiple approaches & solutions to the same problem. It will help you learn and understand SQL in a better way.

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Recommended SQL Courses:

1. Udemy: SQL - MySQL for Data Analytics and Business Intelligence
2. LinkedIn: Master SQL for Data Science
3. edX: Databases: Advanced Topics in SQL
4. edureka: SQL Essentials Training & Certification
5. Coursera: Learn SQL Basics for Data Science
6. Eduonix: SQL Queries

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SQL Problem Statement:

Write a query identifying the type of each record in the TRIANGLES table using its three side lengths. Output one of the following statements for each record in the table:

• Equilateral: It's a triangle with 3 sides of equal length.
• Isosceles: It's a triangle with 2 sides of equal length.
• Scalene: It's a triangle with 3 sides of differing lengths.
• Not A Triangle: The given values of A, B, and C don't form a triangle.

Input Format:

The TRIANGLES table is described as follows:

TRIANGLES Columns

Each row in the table denotes the lengths of each of a triangle's three sides.

Sample Input:

TRIANGLES Sample Data

Sample Output:

Isosceles 
Equilateral 
Scalene 
Not A Triangle

Explanation:

• Values in the tuple (20,20,23) form an Isosceles triangle, because A=B.
• Values in the tuple (20,20,20) form an Equilateral triangle, because A=B=C. 
• Values in the tuple (20,21,22) form a Scalene triangle, because A!=B!=C.
• Values in the tuple (13,14,30) cannot form a triangle because the combined value of sides A and B is not larger than that of side C.

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Solution-1: Using 'AND', 'OR' Clauses(MySQL Query):

SELECT
  CASE
    WHEN (A + B <= C)
    OR (B + C <= A)
    OR (A + C <= B) THEN 'Not A Triangle'
    WHEN (A = B)
    AND (B = C) THEN 'Equilateral'
    WHEN ((A = B) &(A != C))
    OR ((B = C) &(B != A))
    OR ((A = C) &(A != B)) THEN 'Isosceles'
    WHEN (A != B)
    AND (B != C)
    AND (A != C) THEN 'Scalene'
  END AS Triangle_Type
FROM
  TRIANGLES;

NOTE: 

1. Here, the Sequence of When conditions are very important. If you move down the When condition corresponding to 'Not A Trangle' at the bottom, the query will not work as expected.

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Solution-2: Using '&', '|' Operators (MySQL Query):

SELECT
  CASE
    WHEN (A + B <= C) | (B + C <= A) | (A + C <= B) THEN 'Not A Triangle'
    WHEN (A = B) & (B = C) THEN 'Equilateral'
    WHEN ((A = B) & (A != C)) | ((B = C) & (B != A)) | ((A = C) & (A != B)) THEN 'Isosceles'
    WHEN (A != B) & (B != C) & (A != C) THEN 'Scalene'
  END AS Triangle_Type
FROM
  TRIANGLES;

NOTE: 

1. Here, the Sequence of When conditions are very important. If you move down the When condition corresponding to 'Not A Trangle' at the bottom, the query will not work as expected.
   

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Sample Output:

Equilateral
Equilateral
Isosceles
Equilateral
Isosceles
Equilateral
Scalene
Not A Triangle
Scalene
Scalene
Scalene
Not A Triangle
Not A Triangle

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-Akshay P Daga