Databases
Advanced
What is Window Function?
An SQL function that performs calculations across a set of rows related to the current row without collapsing the result set.
Window functions compute values over a "window" of rows defined by OVER(). Unlike GROUP BY, they do not reduce the number of rows. Common functions include ROW_NUMBER(), RANK(), DENSE_RANK(), LAG(), LEAD(), SUM() OVER(), and AVG() OVER().
Example: SELECT name, salary, AVG(salary) OVER(PARTITION BY department) as dept_avg FROM employees. Window functions are essential for running totals, rankings, moving averages, and gap-fill operations.
