What is the concept of SQL window functions?

SQL window functions are advanced functions used for calculating and analyzing data. They can perform aggregation, sorting, ranking, and other operations on specific windows or partitions of the query result set.

Window functions can be used in conjunction with GROUP BY clauses and aggregate functions, but they can also calculate over the entire result set without using a GROUP BY clause. They provide a way to perform calculations on each row, rather than just on the entire result set.

Window functions are typically used in conjunction with an OVER clause, which defines the window’s scope. The window can be defined based on the order of rows, partitions, or other conditions. By using window functions, data within the window can be sorted, aggregated, counted, ranked, etc., and the results can be returned to the query result set.

Common window functions include SUM, AVG, COUNT, MIN, MAX, ROW_NUMBER, RANK, DENSE_RANK, etc. They allow for calculations on data within a window and return the results along with other query columns.