Removing Duplicate Row using SQL (Hive / Impala syntax) - hiveql

Question

I would like to remove duplicate rows based on event_dates and case_ids.
I have a query that looks like this (the query is much longer, this is just to show the problem):
SELECT
event_date,
event_id,
event_owner
FROM eventtable
This gives me results such as the following:
event_date event_id event_owner
2018-02-06 00:00:00 123456 UNASSIGNED
2018-02-07 00:00:00 123456 UNASSIGNED
2018-02-07 00:00:00 123456 Mickey Mouse
2018-02-08 00:00:00 123456 Mickey Mouse
2018-02-09 00:00:00 123456 Minnie Mouse
2018-02-10 00:00:00 123456 Minnie Mouse
2018-02-11 00:00:00 123456 Mickey Mouse
.
.
.
Problem:
I have duplicate entries on 2018-02-07. I would like to have only the second one to remain.
So the result should be this:
event_date event_id event_owner
2018-02-06 00:00:00 123456 UNASSIGNED
2018-02-07 00:00:00 123456 Mickey Mouse
2018-02-08 00:00:00 123456 Mickey Mouse
2018-02-09 00:00:00 123456 Minnie Mouse
2018-02-10 00:00:00 123456 Minnie Mouse
2018-02-11 00:00:00 123456 Mickey Mouse
.
.
.
I've tried to use SELECT DISTINCT ... , but that gives back all the results since it takes into consideration all 3 columns and in that sence all rows are uniqe. I only want to apply DISTINCT on 2 columns event_data and event_id.
Should I use nested sub-queries? Or where lies the truth? All help is much appreciated.

Answer 1

You can use the ROW_NUMBER analytic function for this purpose, but you should clarify the order when you say " I would like to have only the second one to remain". That order doesn't exists in the data, so you need to do something to generate it by yourself.
Try this query:
select event_date, event_id, event_owner
from (
select
row_number() over (partition by event_date order by case when event_owner='UNASSIGNED' then 0 else 1 end desc) as rn,
*
from eventtable
) t
where rn=1