题目如下：

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.

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  form an Isosceles triangle, because . 
Values in the tuple  form an Equilateral triangle, because . Values in the tuple  form a Scalene triangle, because . 
Values in the tuple  cannot form a triangle because the combined value of sides  and  is not larger than that of side .

解题思路：主要是根据三个边长之间的关系来判断三角形的种类，注意判断的顺序是：不是三角形，等边三角形，等腰三角形，其他三角形。

代码如下：

/*
Enter your query here.
*/
select 
case
when (A+B) <= C or (A+C) <= B or (B+C) <= A then 'Not A Triangle'
when (A=B) and (B=C) and (A=C) then 'Equilateral'
when (A=B) or (A=C) or (B=C) then 'Isosceles'
else 'Scalene'
END
from 
TRIANGLES;