All aggregating functions can be used as window functions, 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. The typical use cases for the window functions are computing statistical values of different kinds. Take the car portal database for example. There is a table called advertisement that contains information about the advertisements that users create. Suppose it is required to analyze the quantity of ...
