The SQL ROW_NUMBER() function is a built-in analytical function that assigns a unique sequential number to each row within a result set. It is a window function that is used to return the sequential number of a row within a specific partition of a result set.


The basic syntax for using the ROW_NUMBER() function is:

ROW_NUMBER() OVER (ORDER BY column_name) AS row_num, 
FROM table_name;

In this syntax, the ROW_NUMBER() function is applied over an ordered column specified in the ORDER BY clause. The function returns a sequential integer starting from 1 for each row in the result set.


Here is an example that demonstrates the usage of the ROW_NUMBER() function:

ROW_NUMBER() OVER (ORDER BY salary DESC) AS row_num, 
first_name, last_name, salary 
FROM employees;

In this example, we are retrieving the employee’s first name, last name, and salary from the employees table. The ROW_NUMBER() function is applied to the salary column and orders the result set in descending order based on the salary. The function returns the row number for each employee based on their salary.

The ROW_NUMBER() function is commonly used to rank data within a result set and to paginate data, where you want to retrieve a specific subset of rows from a large result set. By using the ORDER BY clause in conjunction with the ROW_NUMBER() function, you can sort the result set based on a particular column and then retrieve a specific number of rows from that result set.

In conclusion, the SQL ROW_NUMBER() function is a powerful tool that allows you to perform advanced analytical tasks on a result set. It helps in ranking, pagination, and many other use cases.