HackerRank[MySQL] : Type of Triangle

Q

CASE - CASE

SELECT CASE WHEN A + B > C AND B + C > A AND A + C > B THEN # 삼각형 조건 성립
        CASE WHEN A = B AND B = C AND C = A THEN 'Equilateral' 
             WHEN A != B AND B != C AND C!= A THEN 'Scalene'
             ELSE 'Isosceles' END
          ELSE 'Not A Triangle' END
FROM TRIANGLES 

---

CASE - WHEN

SELECT CASE WHEN A + B <= C OR A + C <= B OR B + C <= A 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

GREATEST

SELECT CASE
    WHEN 2 * GREATEST(A, B, C) >= (A + B + C) THEN "Not A Triangle"
    WHEN A = B AND A = C                      THEN "Equilateral"
    WHEN A = B OR A = C OR B = C              THEN "Isosceles"
                                              ELSE "Scalene"
    END
FROM TRIANGLES