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https://issues.apache.org/jira/browse/IMPALA-4741?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Michael Smith updated IMPALA-4741:
----------------------------------
Priority: Critical (was: Major)
> ORDER BY behavior with UNION is incorrect
> -----------------------------------------
>
> Key: IMPALA-4741
> URL: https://issues.apache.org/jira/browse/IMPALA-4741
> Project: IMPALA
> Issue Type: Bug
> Components: Frontend
> Affects Versions: Impala 2.8.0
> Reporter: Greg Rahn
> Priority: Critical
> Labels: correctness, incompatibility, ramp-up, sql-language,
> tpc-ds
> Attachments: query36a.sql, query49.sql
>
>
> When a query uses the UNION, EXCEPT, or INTERSECT operators, the ORDER BY
> clause must be specified at the end of the statement and the results of the
> combined queries are sorted. ORDER BY clauses are not allowed in individual
> branches unless the branch is enclosed by parentheses.
> There are two bugs currently:
> # An ORDER BY is allowed in a branch of a UNION that is not enclosed in
> parentheses
> # The final ORDER BY of a UNION is attached to the nearest branch when it
> should be sorting the combined results of the UNION(s)
> For example, this is not valid syntax but is allowed in Impala
> {code}
> select * from t1 order by 1
> union all
> select * from t2
> {code}
> And for queries like this, the ORDER BY should order the unioned result, not
> just the nearest branch which is the current behavior.
> {code}
> select * from t1
> union all
> select * from t2
> order by 1
> {code}
> If one wants ordering within a branch, the query block must be enclosed by
> parentheses like such:
> {code}
> (select * from t1 order by 1)
> union all
> (select * from t2 order by 2)
> {code}
> Here is an example where incorrect results are returned.
> Impala
> {code}
> [impalad:21000] > select r_regionkey, r_name from region union all select
> r_regionkey, r_name from region order by 1 limit 2;
> +-------------+-------------+
> | r_regionkey | r_name |
> +-------------+-------------+
> | 0 | AFRICA |
> | 1 | AMERICA |
> | 2 | ASIA |
> | 3 | EUROPE |
> | 4 | MIDDLE EAST |
> | 0 | AFRICA |
> | 1 | AMERICA |
> +-------------+-------------+
> Fetched 7 row(s) in 0.12s
> {code}
> PostgreSQL
> {code}
> tpch=# select r_regionkey, r_name from region union all select r_regionkey,
> r_name from region order by 1 limit 2;
> r_regionkey | r_name
> -------------+---------------------------
> 0 | AFRICA
> 0 | AFRICA
> (2 rows)
> {code}
> see also https://cloud.google.com/spanner/docs/query-syntax#syntax_5
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