Any aggregating function can be used as a window function, with the exception of ordered-set and hypothetical-set aggregates. User-defined aggregating functions can also be used as window functions. The presence of the OVER clause indicates that the function is used as a window function.
When the aggregating function is used as a window function, it will aggregate the rows that belong to the window frame of a current row. A typical use case for window functions are computing statistical values of different kinds. Take the car_portal database as an example. The advertisement table contains information about advertisements that users create. Suppose you need to analyze the quantity of advertisements that users create ...
