What is the purpose of SQL window functions?

SQL window functions are used to perform aggregate calculations within the query results without changing the number of rows. They can calculate an aggregate value for each row, instead of aggregating the entire result set. Window functions are typically used in conjunction with GROUP BY and ORDER BY clauses for grouping and sorting operations.

The function of window functions is as follows:

1. Calculate the aggregate value for each row: Window functions can calculate an aggregate value for each row, such as the total amount of each order or the average number of orders for each customer.
2. Sorting: Window functions can sort query results based on specified sorting rules, such as sorting by sales amount, order quantity, and so on.
3. Grouping: Window functions can group query results according to specified grouping rules, such as grouping by customer, product category, and so on.
4. Filtering: Window functions can filter query results based on specified conditions, such as only calculating the number of orders with sales greater than 1000.

In conclusion, SQL window functions can help us perform more flexible, fine-grained aggregations, sorting, and grouping operations on query results, leading to more precise analytical results.