How Can I Efficiently Find the Nth Maximum Salary in a Database?

Identifying the nᵗʰ Maximum Salary in a Salary Table

Finding the third or nᵗʰ maximum salary from a salary table can be a common requirement in various data analysis tasks. To achieve this optimization, several methods can be employed:

Row Number Technique:

This approach involves calculating the row number for each salary value in ascending order and then selecting the salaries corresponding to the desired row numbers (e.g., second and third for n=2 or n=3). The following query demonstrates this:

SELECT Salary, EmpName
FROM
  (
   SELECT Salary, EmpName, ROW_NUMBER() OVER(ORDER BY Salary) AS RowNum
   FROM EMPLOYEE
   ) AS A
WHERE A.RowNum IN (2,3)

Subquery Method:

Another optimization utilizes a subquery to determine the position of the nᵗʰ maximum salary. The subquery counts the number of distinct salaries greater than each employee's salary, and the outer query selects the employee whose salary meets the rank condition:

SELECT *
FROM Employee Emp1
WHERE (N-1) = (
               SELECT COUNT(DISTINCT(Emp2.Salary))
               FROM Employee Emp2
               WHERE Emp2.Salary > Emp1.Salary
               )

Top Keyword Approach:

For this method, a subquery is used to identify the n unique maximum salaries, which is then followed by sorting and selecting the nᵗʰ salary:

SELECT TOP 1 salary
FROM (
      SELECT DISTINCT TOP n salary
      FROM employee
      ORDER BY salary DESC
      ) a
ORDER BY salary

By employing these optimized techniques, the process of retrieving the third or nᵗʰ maximum salary from a salary table becomes more efficient and scalable for large datasets.

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