How to Efficiently Find the Third (or Nth) Maximum Salary in a Database?

Finding Third or nᵗʰ Maximum Salary from Salary Tables Efficiently

In the realm of database management, extracting the third or nᵗʰ maximum salary from a salary table is often a crucial task for data analysis and reporting purposes. To optimize this process, various approaches can be employed.

Row Number Approach:

This technique assigns a row number to each salary value in descending order. By filtering the results to include rows with the specified rank (e.g., 2 or 3), one can directly obtain the desired maximum salary values.

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 Approach:

This method leverages a subquery to determine the count of distinct salary values that exceed the given nᵗʰ maximum salary. By equating this count with (N-1), where N is the desired rank, the query directly retrieves the row corresponding to the nᵗʰ maximum salary.

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

Top Keyword Approach:

This approach utilizes the TOP keyword to directly select the nᵗʰ maximum salary from a subquery that sorts the salaries in descending order. The result is then ordered by salary to extract the desired value.

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

The choice of approach depends on the specific database environment and data volume. The Row Number approach is generally efficient for smaller datasets, while the Subquery and Top Keyword approaches can be more performant for larger datasets.

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