Combine multiple rows into one space separated string

Question

So I have 5 rows like this

userid, col
--------------
1, a
1, b
2, c
2, d
3, e

How would I do query so it will look like this

userid, combined
1, a b
2, c d
3, e

Answer 1

In hive you can use

SELECT userid, collect_set(combined) FROM tabel GROUP BY user_id;

collect_set removes duplicated. If you need to keep them you can check this post:

COLLECT_SET() in Hive, keep duplicates?