how to use order by with collect_set() operation in hive

Question

In Table 1, I have customer_id, item_id and item_rank (rank of item according to some sales). I want to collect a list of items for each customer_id and arrange them according

Answer 1

SELECT customer_id, collect_set(item_id) AS item_list FROM table1 GROUP BY customer_id ORDER BY item_rank

NOTE : Using collect_list() gives you duplicates and collect_set() gives you unique values.