HackerRank - Type of Triangle

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:

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

Sample Input

 

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.

 

 

---

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

else절에서 조건이 여러개 있다면 첫번째 조건에 걸린다면 해당 값들은 다음 조건에서는 취급하지 않는다. 

WHEN절의 순서를 잘 정돈하여 쿼리를 작성하는 것이 중요하다.