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https://issues.apache.org/jira/browse/IMPALA-7785?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Paul Rogers resolved IMPALA-7785.
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Resolution: Invalid
> GROUP BY clause cannot contain a CASE statement
> -----------------------------------------------
>
> Key: IMPALA-7785
> URL: https://issues.apache.org/jira/browse/IMPALA-7785
> Project: IMPALA
> Issue Type: Bug
> Components: Frontend
> Affects Versions: Impala 3.0
> Reporter: Paul Rogers
> Priority: Minor
>
> The FE cannot handle a {{CASE}} statement in a {{GROUP BY}} clause. As a
> result, the change in IMPALA-7655 cannot be applied to queries with such a
> clause for fear of ending up in the situation shown later.
> Consider this simple query:
> {code:sql}
> SELECT case when string_col is not null then string_col else 'foo' end
>
> FROM functional.alltypestiny
> GROUP BY case when string_col is not null then string_col else 'foo' end
>
> {code}
> The above will fail with the following:
> {noformat}
> org.apache.impala.common.AnalysisException:
> select list expression not produced by aggregation output
> (missing from GROUP BY clause?) :
> CASE WHEN string_col IS NOT NULL THEN string_col ELSE 'foo' END
> {noformat}
> This then causes the rewrites in IMPALA-7655 to fail:
> {code:sql}
> SELECT coalesce(string_col, 'foo')
> FROM functional.alltypes
> GROUP BY coalesce(string_col, 'foo')
> {code}
> The above is rewritten using the new conditional function rewrite rules.
> Result:
> {noformat}
> org.apache.impala.common.AnalysisException:
> select list expression not produced by aggregation output
> (missing from GROUP BY clause?):
> CASE WHEN string_col IS NOT NULL THEN string_col ELSE 'foo' END
> {noformat}
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