Windowing functions in Hive are defined using the OVER() clause, which specifies the window or subset of rows over which the function will operate. The window can be defined using a range of methods, including ROWS BETWEEN, RANGE BETWEEN, and UNBOUNDED PRECEDING/FOLLOWING.
Some of the commonly used analytics or windowing functions in Hive include:
- ROW_NUMBER() – assigns a unique number to each row within a partition.
- RANK() – assigns a rank to each row within a partition, with ties receiving the same rank.
- DENSE_RANK() – assigns a rank to each row within a partition, with no gaps in the ranking sequence.
- SUM(), AVG(), MIN(), MAX() – calculate aggregate statistics over a window of rows.
- LAG() and LEAD() – return the value of a column from a previous or subsequent row, respectively.
- FIRST_VALUE() and LAST_VALUE() – return the first or last value in a window, respectively.
Windowing functions can be used in SELECT, WHERE, GROUP BY, and HAVING clauses, among others. They are very useful for complex data analysis and reporting tasks, and can help you gain insights into your data that may not be readily apparent with simple queries.