You are right. I finally solved it but issue with the problem statement is what they say in problem is correct 'triangle inequality' whereas what they are asking for is incorrect. Equality exists for triangle with area zero. So still it is a triangle but zero area (Can be argued otherwise also) but problem statement is wrong.

Would like to correct my statement that triangle with area=0 is still a triangle is incorrect.

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

I do not think so. The table is small so you can look at its contents yourself.

you'll have to check for all the 3 conditions as in (A+B>C AND B+C>A AND C+A>B)

And yet they are stated like rules in the description... I too was stuck as were all these other people. Perhaps you could be a little less stubborn and fix a clearly misleading description.

it's technically only assumed they know sql :P, unless you mean it is word of god? in that case it is whatever you say it is I guess

"It's assumed that anyone attempting this challenge understands basic Geometry".

• Condescending remark, from a stubborn Mod. Learn to take criticism and improve.

I've come here to learn/revise sql, not learn/revise geometry. I think it's odd that the rules at the top cover the basic triangle types that most of us would remember from school, but not the triangle inequality stuff that fewer of us would recall, yet which is only alluded to by example. I didn't know about the latter at all (or had clean forgotten) and just added an 'else' for it.

My solution:

SELECT IF((A+ B) > C and (A + C)> B and (B + C) > A ,
            IF(A = B and A = C and C=B,'Equilateral',
                IF(A=B OR B = C OR A = C,'Isosceles','Scalene'))
        ,'Not A Triangle') TRIANGLES
FROM TRIANGLES

Thank you! Makes sense now becuase it was expecting that output

This was the missing piece of the puzzle for me also! I've been spending at least an hour trying to figure out why it wasn't testing correctly. This was it.

Yeah, the check for a correct solution clearly needs to be fixed to accept 'Not a Triangle', since the word 'a' is never capitalized unless it's the first word in a sentence.

Thanks! I did the same mistake.

Sum of 2 sides of a triangle should always be greater than the 3rd side. So we are checking the three possiblities for 3 pairs of sides

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...

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!

sigh took me a while to realize I needed single quotes

agreed. It will be great if someone could correct the typos.

yeah but a lot of these problems have semantic errors that cause me aggravation and wondering, why my apparently correct answer is wrong.

It was correct as it was before. Articles (a, an, etc.) should not be capitalized in a title.

Thank you so much, but for Equilateral, you only need to write 2 conditions, like a=b and a=c would be enough.

that was my problem, I needed to check for "Not A Triangle" condition first

SELECT "Isosceles" from TRIANGLES where ( ((A = B) or (A = C) or (C = B) ) and not ( A = B and A = C ) and not (( (A + B) < C ) or ( (C + B) < A ) or ( (C + A) < B )) );

SELECT "Equilateral" from TRIANGLES where ( A = B and A = C );

SELECT "Scalene" from TRIANGLES where ( ((A <> B) and (A <> C) and ( B <> C )) and not (( (A + B) < C ) or ( (C + B) < A ) or ( (C + A) < B )) );

SELECT "Not A Triangle" from TRIANGLES where (( (A + B) < C ) or ( (C + B) < A ) or ( (C + A) < B ));

Why does it says wrong answer ??

or this

CASE WHEN (((A = B) or (A = C) or (C = B) ) and not ( A = B and A = C ) and not (( (A + B) < C ) or ( (C + B) < A ) or ( (C + A) < B ))) THEN SELECT "Isosceles"; WHEN ( A = B and A = C ) THEN SELECT "Isosceles"; WHEN (((A <> B) and (A <> C) and ( B <> C )) and not (( (A + B) < C ) or ( (C + B) < A ) or ( (C + A) < B ))) THEN SELECT "Scalene"; WHEN (( (A + B) < C ) or ( (C + B) < A ) or ( (C + A) < B )) THEN SELECT "Not A Triangle"; END CASE

case when a+b-c=c then 'equilateral'---what is wrong in this logic.. plz help

I tried this, which worked when I set the problem up on my own MySQL but failed the code test. Anyone know why?

select case when A>=B+C or B>A+C or C>=A+B then 'Not a triangle' when A=B and B=C then 'Equilateral' when A=B and B != C then 'Isosceles' when A!=B and B!=C and A!=C then 'Scalene' end as Type from triangles;