The syntax of the window functions is as follows:
<function_name> (<function_arguments>)OVER( [PARTITION BY <expression_list>] [ORDER BY <order_by_list>] [<frame_clause>])
The construct in the parentheses after the OVER keyword is called the window definition.
Window functions, in general, work like aggregating functions. They process sets of records. These sets are built separately for each processed record and can overlap. That's why, unlike the normal aggregating functions, window functions are evaluated for each row.
For each record, a set of rows to be processed by a window function is built in the following way: at the beginning, the PARTITION BY clause is processed. All the records that have the same values after ...
