方法一:
SELECT IFNULL( ( SELECT DISTINCT Salary FROM Employee ORDER BY Salary DESC LIMIT 1 OFFSET 1 ), NULL ) AS SecondHighestSalary;
方法二:
SELECT MAX(Salary) AS SecondHighestSalary FROM Employee WHERE Salary < ( SELECT MAX(Salary) FROM Employee );
方法一:
SELECT IFNULL( ( SELECT DISTINCT Salary FROM Employee ORDER BY Salary DESC LIMIT 1 OFFSET 1 ), NULL ) AS SecondHighestSalary;
方法二:
SELECT MAX(Salary) AS SecondHighestSalary FROM Employee WHERE Salary < ( SELECT MAX(Salary) FROM Employee );