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  1. Practice
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  4. Type of Triangle
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Type of Triangle

  • Unremarkable + 3 comments
    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
    • elliott_j_harri1 + 1 comment

      I had very similar code but I put the 'Iscoceles' case statment before the 'Not a Triangle' one and it caused an error. The order in which you check the statments can really reduce the logic in your code :)

      SELECT CASE WHEN 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 AS 'Triangles' FROM TRIANGLES;

      • antoniro + 1 comment

        Exactly! I have been saying that in few comments!

        You don't need to have multiple CASE statements next to each other or nested CASEs. If you check the conditions in the right order, only one CASE statement with multiple WHENs will do the job:

        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

        I think this is the cleanest and shortest answer...

        • veerankisatya80 + 0 comments

          When the Isosceles and Equilateral case statements order are reversed, that is the Equi is checked after Isos then the test case fails. Is it a necessaity to do this in this ordeR?

    • codegritty + 1 comment

      Hello, can you please explaing this... 

      WHEN 2 * GREATEST(A, B, C) >= (A + B + C)

      Thank you in advance!

      • antoniro + 2 comments

        The general rule/condition for a valid triangle is that the longest side should be less than the sum of the two other sides:

        longestSide < sumOfOtherSides (1)

        For example, if you have A, B, and C, where B is the longest side, then the condition B < (A+C) is true for a valid triangle, and false otherwise.

        Now, the sum of all the sides of the triangle is (A+B+C). Given B is the longest side, if you want to get the sum of other sides, you have to remove B from the sum of all sides, thus (A+C) = (A+B+C) - (B) or in other words:

        sumOfOtherSides = sumOfAllSides - longestSide (2)

        With this in mind, the first inequation (1) can now be written as :

        longestSide < sumOfAllSides - longestSide

        which is equivalent to

        longestSide + longestSide < sumOfAllSides

        or

        2 * longestSide < sumOfAllSides (3)

        So, a triangle is valid if and only if inequation (3) is true. If (3) is false, then we have 2 * longestSide >= sumOfAllSides. In MySQL and Oracle SQL, the GREATEST() function returns the greatest value of the guiven arguments. Hence, you have longestSide = GREATEST(A, B, C).

        Everything above put together, the final formula to check if a triangle is NOT valid is :

        2 * GREATEST(A, B, C) >= (A + B + C)

        Hope my explanation was clear and detailed!

        • pragya_maheshwa1 + 0 comments
          [deleted]
        • MAbdElRaouf + 0 comments

          Thank you for sharing this information.

    • rishilja + 1 comment

      This fails in Oracle due to double quote: "" I'd advise to use '' as standard for strings an dates.

      • mahdi2 + 0 comments

        sigh took me a while to realize I needed single quotes