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https://issues.apache.org/jira/browse/CALCITE-3128?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16874592#comment-16874592
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Danny Chan commented on CALCITE-3128:
-------------------------------------
[~julianhyde] thanks,
{quote}if the condition is '(t1.c is null) = (t2.c is null)', I think the
problem would still occur.
{quote}
I checked this query:
{code:sql}
select dept.deptno, emp.ename
from dept join emp
on (dept.dname is null) = (emp.sal is null)
order by emp.ename limit 10;
{code}
and finally plan is
{code:xml}
EnumerableLimit(fetch=[10])
EnumerableSort(sort0=[$1], dir0=[ASC])
EnumerableCalc(expr#0..4=[{inputs}], DEPTNO=[$t0], ENAME=[$t3])
EnumerableHashJoin(condition=[=($1, $4)], joinType=[inner])
EnumerableCalc(expr#0..2=[{inputs}], expr#3=[IS NULL($t1)],
DEPTNO=[$t0], $f3=[$t3])
EnumerableTableScan(table=[[scott, DEPT]])
EnumerableCalc(expr#0..7=[{inputs}], expr#8=[IS NULL($t5)],
proj#0..1=[{exprs}], $f8=[$t8])
EnumerableTableScan(table=[[scott, EMP]])
{code}
The condition '(t1.c is null) = (t2.c is null)' for hash join are all boolean
keys, which means they will never be null, so i don't think there is any
problem for this case.
{quote}The key factor, I think, is that one side has just one column, and a
null in that column.
{quote}
This is not true, like the case:
{code:sql}
SELECT *
FROM (VALUES (NULLIF(5, 5)), (NULLIF(5, 5))) a, (VALUES (NULLIF(5, 5)),
(NULLIF(5, 5))) b
{code}
> Joining two tables producing only NULLs will return 0 rows
> ----------------------------------------------------------
>
> Key: CALCITE-3128
> URL: https://issues.apache.org/jira/browse/CALCITE-3128
> Project: Calcite
> Issue Type: Bug
> Components: core
> Affects Versions: 1.20.0
> Reporter: Muhammad Gelbana
> Assignee: Danny Chan
> Priority: Major
> Labels: pull-request-available
> Time Spent: 2h 10m
> Remaining Estimate: 0h
>
> The following queries will return 0 rows while they're expected to ruturn
> rows with NULLs in them.
> {code:sql}
> SELECT *
> FROM (SELECT NULLIF(5, 5)) a, (SELECT NULLIF(5, 5)) b
> {code}
> {code:sql}
> SELECT *
> FROM (VALUES (NULLIF(5, 5)), (NULLIF(5, 5))) a, (VALUES (NULLIF(5, 5)),
> (NULLIF(5, 5))) b
> {code}
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