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https://issues.apache.org/jira/browse/CALCITE-1016?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15051581#comment-15051581
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Laljo John Pullokkaran commented on CALCITE-1016:
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[~julianhyde] Group by constant on an empty table should return no rows.
hive> select count(*) from gbt1;
Total MapReduce CPU Time Spent: 0 msec
OK
0
Time taken: 4.846 seconds, Fetched: 1 row(s)
hive> select count(*) from gbt1 group by 1;
OK
Time taken: 1.503 seconds
> What should "GROUP BY 1" return on an empty table?
> --------------------------------------------------
>
> Key: CALCITE-1016
> URL: https://issues.apache.org/jira/browse/CALCITE-1016
> Project: Calcite
> Issue Type: Bug
> Reporter: Julian Hyde
> Assignee: Julian Hyde
>
> What should "GROUP BY 1" return on an empty table? Calcite currently returns
> 0 rows. I am hearing claims that according to standard SQL it should return 1
> row.
> Here is what Oracle 11.2.0.2.0 does.
> {noformat}
> SQL> select count(*) from emp where 1 = 0;
> COUNT(*)
> ----------
> 0
> SQL> select count(*) from emp where 1 = 0 group by ();
> no rows selected
> SQL> select count(*) from emp where 1 = 0 group by 1;
> no rows selected
> SQL> select count(*) from emp;
> COUNT(*)
> ----------
> 14
> SQL> select count(*) from emp group by ();
> COUNT(*)
> ----------
> 14
> SQL> select count(*) from emp group by 1;
> COUNT(*)
> ----------
> 14
> {noformat}
> I had expected {code}select count(*) from emp where 1 = 0 group by (){code}
> would return 1 row, but it returns 0, like {code}group by 1{code}.
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