There are three common methods to find the Nth highest value of a column in SQL. 1. Use subquery and LIMIT/OFFSET: First sort the target column in descending order, skip the first N-1 record and then take one. It is suitable for simple scenarios but may affect performance; 2. Exclude maximum values ??layer by layer through nested subqueries: the logic is clear but the structure is complex when the hierarchy increases; 3. Use DENSE_RANK or ROW_NUMBER window function (recommended): Flexible processing of duplicate values, supports precise ranking, and is suitable for database environments that support window functions. Which method to choose depends on the specific database type, data volume and structural requirements.

Finding the Nth highest value of a column in SQL, such as "second highest salary", is not a problem that can be solved simply by taking the maximum value or sorting it. The key is how to skip the previous few maximum values ??and then get out exactly what you want.

Methods using subquery and LIMIT/OFFSET

This is one of the most common and easy to understand methods. The basic idea is: first sort the target column in descending order, then skip the first N-1 record, and then take one.

 SELECT sales
FROM employees
ORDER BY salary DESC
LIMIT 1 OFFSET N-1;

For example, to check the second highest salary:

 SELECT sales
FROM employees
ORDER BY salary DESC
LIMIT 1 OFFSET 1;

Note: This method may be a bit slow when the data volume is large or N is large, and if there are duplicate values ??(such as two identical wages), it will still skip the specified number of rows.

Exclude maximum values ??using subqueries

If you don't want to use LIMIT and OFFSET , you can also exclude the maximum values ??one by one through nested queries. For example, if you want to find the second highest salary, you can write this:

 SELECT MAX(salary)
FROM employees
WHERE salary < (SELECT MAX(salary) FROM employees);

The advantage of this method is that it is clear logic and there will be no pagination offset. But the disadvantage is that every time you add a level (such as looking for the third highest), you need to have an extra layer of subquery, which will become more complicated.

For example, find the third highest salary:

 SELECT MAX(salary)
FROM employees
WHERE salary < (
    SELECT MAX(salary)
    FROM employees
    WHERE salary < (SELECT MAX(salary) FROM employees)
);

Use the DENSE_RANK or ROW_NUMBER window function (recommended)

If you are using a database that supports window functions (such as MySQL 8.0, PostgreSQL, SQL Server, Oracle, etc.), this method is the most flexible and recommended.

Take DENSE_RANK() as an example:

 SELECT sales
FROM (
    SELECT salary, DENSE_RANK() OVER (ORDER BY salary DESC) AS rnk
    FROM employees
) ranked
WHERE rnk = N;

This can avoid the problem of ranking jumps due to duplicate values. For example, when two are tied for first place, DENSE_RANK() will continue to rank the next value to 2, while RANK() will jump to 3.

If you want to count as a ranking even if there are multiple identical values, use DENSE_RANK() ; if you want to skip these duplicate rankings, use RANK() .

Basically these are the methods. Different scenarios can be used to choose different methods: subquery exclusion method can be used for simple queries, and window functions are recommended for large data sets. If compatibility requirements are high, LIMIT OFFSET can also be considered. Which one is suitable depends on your specific database environment and data structure.

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