SQL练习 2022/7/1

176. 第二高的薪水

题干
代码思路

1. 使用子查询和 LIMIT 子句

select
(
    select distinct salary
    from employee
    order by salary desc
    limit 1 offset 1
) as SecondHighestSalary

2. 使用 IFNULL 和 LIMIT 子句

SELECT
    IFNULL(
      (SELECT DISTINCT Salary
       FROM Employee
       ORDER BY Salary DESC
        LIMIT 1 OFFSET 1),
    NULL) AS SecondHighestSalary

3. 使用max函数
   比第一大的就是第二大

select max(salary) as SecondHighestSalary
from employee
where salary<(select max(salary) from employee)

177. 第N高的薪水

题干
代码思路

1. 使用limit函数

CREATE FUNCTION getNthHighestSalary(N INT) RETURNS INT
BEGIN
    SET N := N-1;
  RETURN (
      # Write your MySQL query statement below.
      select
        (
            select distinct salary
            from employee
            order by salary desc
            limit 1 offset N
        ) as SecondHighestSalary
    );
END

2. 使用窗口函数

CREATE FUNCTION getNthHighestSalary(N INT) RETURNS INT
BEGIN
  RETURN (
      # Write your MySQL query statement below.
        SELECT 
            DISTINCT salary
        FROM 
            (SELECT 
                salary, dense_rank() over(ORDER BY salary DESC) AS rnk
             FROM 
                employee) tmp
        WHERE rnk = N
  );
END

3. 其他
   力扣官方题解