How do you use a window function with DENSE_RANK to rank salaries within each department and filter for rank 2?

DENSE_RANK is a window function that assigns the same rank to rows with identical values and skips no numbers when ties occur. In the query you partition by department_id so each department gets its own ranking, order by salary descending so the highest salary gets rank 1, and then you filter for rnk = 2 to get the second distinct salary. The key difference from ROW_NUMBER is that if two employees share the top salary, both get rank 1 and the next distinct salary is rank 2, not 3. This is useful when you need the second highest distinct salary per department.