sql - 第二高薪水

Question

编写SQL查询，从Employee表中获取第二高的薪水。

    | Id | Salary |
    | 1  | 100    |
    | 2  | 200    |
    | 3  | 300    |

例如，给定上面的 Employee 表，查询应该返回 200 作为第二高的薪水。如果没有第二高的薪水，则查询应返回 null。

    | SecondHighestSalary |
    | 200                 |

这是Leetcode的一道题，我输入了如下代码:

    SELECT CASE WHEN Salary = '' 
                THEN NULL
    ELSE Salary 
    END AS SecondHighestSalary 
    FROM (SELECT TOP 2 Salary
                ,ROW_NUMBER() OVER (ORDER BY Salary DESC) AS Num
          FROM Employee
          ORDER BY Salary DESC) AS T
    WHERE T.Num = 2

它表示如果没有第二高薪水的值，查询不会返回 NULL。 例如。如果表格是

   | Id | Salary| 
   | 1  |  100  |

查询应该返回

   |SecondHighestSalary|
   |       null        |

而不是

   |SecondHighestSalary|
   |                   |

Answer 1

Leetcode 2nd highest salary 问题的解决方案是:

Select 
    Max(Salary) AS SecondHighestSalary 
from Employee 
    where Salary < (
                     Select Max(Salary) from Employee
                   );