Question

176. Second Highest Salary

中文文档

Description

Table: Employee

+-------------+------+
| Column Name | Type |
+-------------+------+
| id      | int  |
| salary    | int  |
+-------------+------+
id is the primary key (column with unique values) for this table.
Each row of this table contains information about the salary of an employee.

 

Write a solution to find the second highest salary from the Employee table. If there is no second highest salary, return null (return None in Pandas).

The result format is in the following example.

 

Example 1:

Input: 
Employee table:
+----+--------+
| id | salary |
+----+--------+
| 1  | 100  |
| 2  | 200  |
| 3  | 300  |
+----+--------+
Output: 
+---------------------+
| SecondHighestSalary |
+---------------------+
| 200         |
+---------------------+

Example 2:

Input: 
Employee table:
+----+--------+
| id | salary |
+----+--------+
| 1  | 100  |
+----+--------+
Output: 
+---------------------+
| SecondHighestSalary |
+---------------------+
| null        |
+---------------------+

Solutions

Solution 1: Use Sub Query and LIMIT

import pandas as pd


def second_highest_salary(employee: pd.DataFrame) -> pd.DataFrame:
  # Drop any duplicate salary values to avoid counting duplicates as separate salary ranks
  unique_salaries = employee["salary"].drop_duplicates()

  # Sort the unique salaries in descending order and get the second highest salary
  second_highest = (
    unique_salaries.nlargest(2).iloc[-1] if len(unique_salaries) >= 2 else None
  )

  # If the second highest salary doesn't exist (e.g., there are fewer than two unique salaries), return None
  if second_highest is None:
    return pd.DataFrame({"SecondHighestSalary": [None]})

  # Create a DataFrame with the second highest salary
  result_df = pd.DataFrame({"SecondHighestSalary": [second_highest]})

  return result_df

# Write your MySQL query statement below
SELECT
  (
    SELECT DISTINCT salary
    FROM Employee
    ORDER BY salary DESC
    LIMIT 1, 1
  ) AS SecondHighestSalary;

Solution 2: Use MAX() function

# Write your MySQL query statement below
SELECT MAX(salary) AS SecondHighestSalary
FROM Employee
WHERE salary < (SELECT MAX(salary) FROM Employee);

Solution 3: Use IFNULL() and window function

# Write your MySQL query statement below
WITH T AS (SELECT salary, DENSE_RANK() OVER (ORDER BY salary DESC) AS rk FROM Employee)
SELECT (SELECT DISTINCT salary FROM T WHERE rk = 2) AS SecondHighestSalary;