Hackerrank - SQL - What Type of Triangle

#sql #learning

Repo

Problem Description

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:

Column	Type
A	INTEGER
B	INTEGER
C	INTEGER

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

Solution Approach

Use a CASE statement to evaluate the triangle type based on the following conditions:

Check if the sides can form a triangle (sum of any two sides must be greater than the third side)
If it's a triangle, determine its type:
- Equilateral: all three sides are equal
- Isosceles: exactly two sides are equal
- Scalene: no sides are equal

Step-by-Step Explanation

Start with a SELECT statement using CASE to evaluate different conditions:

   SELECT CASE

First, check if the sides can form a triangle:

   WHEN (A + B <= C) OR (B + C <= A) OR (C + A <= B) THEN 'Not A Triangle'

If it's a triangle, check if it's equilateral (all sides equal):

   WHEN A = B AND B = C THEN 'Equilateral'

If it's not equilateral, check if it's isosceles (exactly two sides equal):

   WHEN A = B OR A = C OR B = C THEN 'Isosceles'

If it's neither equilateral nor isosceles, it must be scalene:

   ELSE 'Scalene'

Close the CASE statement and specify the table:

   END
   FROM TRIANGLES

The final query:

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