MySQL：嵌套的更好解决方案

Question

我有链接： Types Of Triangle

我的回答是：

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

到目前为止，它是正确的但不知何故我使用了凌乱的嵌套 IF 。

我的问题是，在优雅和效率方面有更好的解决方法吗？我多年来对SQL查询很熟悉，但由于我更喜欢​​前端开发，所以我很少使用它。

感谢。

Answer 1

您需要使用CASE语句而不是IF：

SELECT 
CASE WHEN (A = B AND A = C) then 'Equilateral'
WHEN ((A = B OR A = C OR B = C) AND (A + B) > C) then 'Isosceles'
WHEN (A != B AND A != C AND B != C AND (A + B) > C) then 'Scalene'
ELSE 'Not A Triangle'
END AS "Type of Triangle"
FROM TRIANGLES

Answer 2

您可以使用CASE：

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