Second Highest Salary in MySQL and SQL Server - LeetCode Solution

Write a SQL query to get the second highest salary from the Employee table.

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

For example, given the above Employee table, the second highest salary is 200. If there is no second highest salary, then the query should return NULL. You can write SQL query in any of your favorite databases e.g. MySQL, Microsoft SQL Server, or Oracle. You can also use database specific feature e.g. TOP, LIMIT or ROW_NUMBER to write SQL query, but you must also provide a generic solution which should work on all database. 

In fact, there are several ways to find the second highest salary and you must know a couple of them e.g. in MySQL without using the LIMIT keyword, in SQL Server without using TOP, and in Oracle without using RANK and ROWNUM. 

Once you solve the problem, the Interviewer will most likely increase the difficulty level by either moving to the Nth salary direction or taking away these built-in utilities.

Second Highest Salary in MySQL without LIMIT

Here is a generic SQL query to find the second highest salary, which will also work fine in MySQL. This solution uses a subquery to first exclude the maximum salary from the data set and then again finds the maximum salary, which is effectively the second maximum salary from the Employee table.

SELECT MAX(salary) FROM Employee 
WHERE Salary NOT IN ( SELECT Max(Salary) FROM Employee);

This will return 200 in our case.

Here is another solution that uses sub query but instead of IN clause it uses < operator

SELECT MAX(Salary) From Employee
 WHERE Salary < ( SELECT Max(Salary) FROM Employee);

You can use this SQL query if the Interviewer ask you to get second highest salary in MySQL without using LIMIT.  You can also use distinct keyword if your Employee table may contain duplicate salary, In this example there is no such record, so I have not used distinct.

Second Highest Salary using Correlated SubQuery

Previous SQL query was also using subquery but it was non-correlated, this solution will use a correlated subquery. This is also a generic solution to find Nth highest salary in the Employee table. 

For each record processed by outer query, inner query will be executed and will return how many records has records has salary less than the current salary. If you are looking for second highest salary then your query will stop as soon as inner query will return 2.

SELECT Id, Salary
FROM Employee e
WHERE 2=(SELECT COUNT(DISTINCT Salary) FROM Employee p
WHERE e.Salary<=p.Salary)

By the way, If you don't know the difference between correlated and non-correlated subquery, see here.

Second Maximum Salary in MySQL using LIMIT

MySQL has a special keyword called LIMIT which can be used to limit the result set e.g. it will allow you to see the first few rows, last few rows, or range of rows. You can use this keyword to find the second, third or Nth highest salary. Just use order by clause to sort the result set then print the second salary as shown below :

SELECT Salary FROM 
  (SELECT Salary FROM Employee ORDER BY salary DESC LIMIT 2) AS Emp 
ORDER BY salary LIMIT 1;

In this solution, we have first sorted all salaries from the Employee table in decreasing order, so that the 2 highest salaries come at top of the result set. After that, we took just two records by using LIMIT 2. 

Again we did the same thing but this time we sort the result set in ascending order so that the second-highest salary comes at the top. Now we print that salary by using LIMIT 1. Simple and easy, right?

Second Highest Salary using SQL Server Top Keyword

Just like MySQL has LIMIT keyword, which is immensely helpful in sorting and paging, Microsoft SQL Server also has a special keyword called TOP, which as name suggest prints top records from result set. You can print top 10 records by saying TOP 10. 

I frequently use this keyword to see the data from a large table, just to understand columns and data inside it. Here is the SQL query to find second maximum salary in SQL Server :

SELECT TOP 1 Salary FROM 
( SELECT TOP 2 Salary FROM Employee ORDER BY Salary DESC) AS MyTable 
ORDER BY Salary ASC;

Here is the output of the above query running on Microsoft SQL Server 2014 :

Now It's time to apply the knowledge you have learned so far. Solve following SQL queries at your convenience :

1. Write SQL query to get a third highest salary from Employee table?
2. How do you find the 4th highest salary in MySQL without using the LIMIT keyword?
3. Write SQL query to find second highest salary in Oracle database using ROWNUM?
4. How to find Nth highest salary in SQL Server without using TOP keyword?
5. Find the second highest salary in Oracle using rank?
6. How to find the top 3 salaries in Oracle without using ROW_NUMBER or RANK()?

Now, let's see the answers for few questions

1. Write SQL query to get a third highest salary from Employee table?

To retrieve the third-highest salary from the Employee table, you can use the following SQL query:

SELECT DISTINCT Salary

FROM Employee

ORDER BY Salary DESC

LIMIT 1 OFFSET 2;

This query selects distinct salary values from the Employee table, orders them in descending order (highest to lowest), and then uses the LIMIT and OFFSET clauses to skip the first two rows and retrieve the third-highest salary. Adjust the table and column names according to your actual database schema.

2. How do you find the 4th highest salary in MySQL without using the LIMIT keyword?

To find the 4th highest salary in MySQL without using the LIMIT keyword, you can use a subquery with the DISTINCT keyword along with the ORDER BY clause. Here's an example SQL query:

SELECT MAX(Salary) AS FourthHighestSalary

FROM Employee

WHERE Salary NOT IN (

    SELECT DISTINCT Salary

    FROM Employee

    ORDER BY Salary DESC

    LIMIT 3

);

This query uses a subquery to get the top three distinct salary values, and then filters out those salaries in the outer query, effectively retrieving the fourth highest salary. Make sure to replace Employee with the actual table name and adjust column names accordingly based on your database schema.

That's all about different ways to find the Second highest Salary in MySQL and SQL Server.  We have seen examples to get the second highest salary in MySQL by using LIMIT and without using LIMIT. Similarly in MSSQL, we know how to get the second highest salary by using TOP and without using the TOP keyword. 

I have left the Oracle database for you as an exercise. If you are able to find solutions to all the above SQL queries in a quick time and feeling bore again, check out my post about the Top 20 SQL queries from Interviews for some more fun.