What is the output of the ROW_NUMBER() function in SQL?

The ROW_NUMBER() function assigns a unique sequential integer to rows within a result set, starting at 1 for the first row in each partition. It is defined as ROW_NUMBER() OVER (PARTITION BY ... ORDER BY ...). For example, if you have a table of employees with columns Department and Salary, you can use ROW_NUMBER() OVER (PARTITION BY Department ORDER BY Salary DESC) to rank employees within each department by salary. The output will be a new column containing the rank for each row. It does not affect the underlying data; it only adds a computed column to the result set.