Window functions

Window functions, available since Hive v0.11.0, are a special group of functions that scan multiple input rows to compute each output value. Window functions are usually used with OVER, PARTITION BY, ORDER BY, and the windowing specification. Different from the regular aggregate functions used with the GROUP BY clause, and limited to one result value per group, window functions operate on windows where the input rows are ordered and grouped using flexible conditions expressed through an OVER and PARTITION clause. Window functions give aggregate results, but they do not group the result set. They return the group value multiple times with each record. Window functions offer great flexibility and functionalities compared term the regular GROUP BY clause and make special aggregations by HQL easier and more powerful. The syntax for a window function is as follows...