What are window functions in Spark SQL?

In Spark SQL, window functions are a special type of function that can be used to calculate results within specific windows or partitions. Window functions are commonly used for tasks such as ranking, aggregating, and sorting data that require grouping and calculations. By using window functions, data can be manipulated and analyzed more flexibly without affecting the original data ordering or grouping. Common window functions include ROW_NUMBER, RANK, SUM, AVG, and more. Spark SQL supports the use of window functions to process large datasets, offering a variety of built-in window functions as well as the ability to create custom window functions.