MySQL CASE and tuple method

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'
    WHEN A != B and B != C THEN 'Scalene'
  END tuple
FROM TRIANGLES;

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