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https://issues.apache.org/jira/browse/IMPALA-7782?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Work on IMPALA-7782 started by Tim Armstrong.
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> discrepancy in results with a subquery containing an agg that produces an
> empty set
> -----------------------------------------------------------------------------------
>
> Key: IMPALA-7782
> URL: https://issues.apache.org/jira/browse/IMPALA-7782
> Project: IMPALA
> Issue Type: Bug
> Components: Frontend
> Affects Versions: Impala 2.12.0, Impala 3.1.0
> Reporter: Michael Brown
> Assignee: Tim Armstrong
> Priority: Major
> Labels: correctness, query_generator, ramp-up
>
> A discrepancy exists between Impala and Postgres when a subquery contains an
> agg and results in an empty set, yet the WHERE clause looking at the subquery
> should produce a "True" condition.
> Example queries include:
> {noformat}
> USE functional;
> SELECT id
> FROM alltypestiny
> WHERE -1 NOT IN (SELECT COUNT(id) FROM alltypestiny HAVING false);
> SELECT id
> FROM alltypestiny
> WHERE NULL NOT IN (SELECT COUNT(id) FROM alltypestiny HAVING false);
> SELECT id
> FROM alltypestiny
> WHERE (SELECT COUNT(id) FROM alltypestiny HAVING false) IS NULL;
> {noformat}
> These queries do not produce any rows in Impala. In Postgres, the queries
> produce all 8 rows for the functional.alltypestiny id column.
> Thinking maybe there were Impala and Postgres differences with {{NOT IN}}
> behavior, I also tried this:
> {noformat}
> USE functional;
> SELECT id
> FROM alltypestiny
> WHERE -1 NOT IN (SELECT 1 FROM alltypestiny WHERE bool_col IS NULL);
> {noformat}
> This subquery also produces an empty set just like the subquery in the
> problematic queries at the top, but unlike those queries, this full query
> returns the same results in Impala and Postgres (all 8 rows for the
> functional.alltypestiny id column).
> For anyone interested in this bug, you can migrate data into postgres in a
> dev environment using
> {noformat}
> tests/comparison/data_generator.py --use-postgresql --migrate-table-names
> alltypestiny --db-name functional migrate
> {noformat}
> This is in 2.12 at least, so it's not a 3.1 regression.
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