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https://issues.apache.org/jira/browse/IMPALA-9877?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17143076#comment-17143076
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Tim Armstrong commented on IMPALA-9877:
---------------------------------------
Thanks [~koke], such clear bug reports are valuable.
> uuid() generates multiple values per row when joined from a CTE
> ---------------------------------------------------------------
>
> Key: IMPALA-9877
> URL: https://issues.apache.org/jira/browse/IMPALA-9877
> Project: IMPALA
> Issue Type: Bug
> Affects Versions: Impala 2.12.0
> Environment: impalad version 2.12.0-cdh5.16.1 RELEASE (build
> 4a3775ef6781301af81b23bca45a9faeca5e761d)
> Reporter: Jorge Bernal
> Priority: Major
>
> I'm not sure if I'm misunderstanding the execution model here, but I would
> expect that when I use uuid() on a CTE, it returns a different value for each
> row of the CTE, and not one value per row of the final join.
> It's hard to explain, so here's an example:
>
> {code:java}
> drop table if exists events;
> create table events (uid int, ts int);
> insert into events values (1,1), (2,2), (1,3);
> +-----+----+
> | uid | ts |
> +-----+----+
> | 1 | 1 |
> | 2 | 2 |
> | 1 | 3 |
> +-----+----+{code}
>
> If you then use uuid() on a CTE, and join it with something else, the
> resulting values might have a different uuid for the same input row:
> {code:java}
> with sessions as (
> select
> uid,
> uuid() session_id,
> min(ts) session_start
> from events
> group by uid
> )
> select
> session_id,
> events.*
> from sessions join events on sessions.uid = events.uid;
> drop table if exists koke_events;
> +--------------------------------------+-----+----+
> | session_id | uid | ts |
> +--------------------------------------+-----+----+
> | 71d3671a-fa97-4c00-8d90-d1584ad7cf18 | 2 | 2 |
> | af564c03-2db3-44cb-bf5b-7748e231af72 | 1 | 3 |
> | d4bc2779-1bd9-4a5e-a5e2-dc28b00d2f34 | 1 | 1 |
> +--------------------------------------+-----+----+
> {code}
> I would expect that rows with the same {{uid}} would have the same
> {{session_id}} in this result.
> When I run the same query in Hive, that's the behavior:
> {code:java}
> +---------------------------------------+-------------+------------+--+
> | session_id | events.uid | events.ts |
> +---------------------------------------+-------------+------------+--+
> | e39555b2-c99b-4521-bfb4-9c4d0a5fd3cc | 1 | 1 |
> | e39555b2-c99b-4521-bfb4-9c4d0a5fd3cc | 1 | 3 |
> | 72f8a922-738e-4151-ba93-3b5e50eb9140 | 2 | 2 |
> +---------------------------------------+-------------+------------+--+
> {code}
>
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