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https://issues.apache.org/jira/browse/CALCITE-2602?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16634458#comment-16634458
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Julian Hyde commented on CALCITE-2602:
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It doesn't seem to be a very useful feature. Instead of {code} select * from
emp join dept where emp.deptno = dept.deptno{code} you can write {code}select *
from emp cross join dept where emp.deptno = dept.deptno{code} or {code} select
* from emp, dept where emp.deptno = dept.deptno{code}
As it is non-standard and has two standard alternatives, I think this would be
better in Babel than in Calcite's core parser.
It looks as if the syntax is ambiguous; in {code}select * from emp join dept
join location on dept.locationId = location.locationId{code} it is not clear
whether the {{on}} clause applies to {{(emp join dept) join location}} or just
{{dept join location}}. A similar ambiguity, called a shift-reduce conflict,
occurs in languages in the C family, including Java: {code}if (e1) if (e2) s1
else s2{code} could be resolved to either {code} if (e1) { if (e2) s1 } else
s2{code} or to{code}if (e1) { if (e2) s1 else s2 }{code} but by convention is
resolved to the latter. That ambiguity might make the parser a bit harder to
write, and we would need to specify which behavior we intend, and write tests
for it.
> Support inner join without on-condition
> ---------------------------------------
>
> Key: CALCITE-2602
> URL: https://issues.apache.org/jira/browse/CALCITE-2602
> Project: Calcite
> Issue Type: Bug
> Components: core
> Affects Versions: 1.17.0
> Reporter: pengzhiwei
> Assignee: Julian Hyde
> Priority: Major
>
> Currently,calcite cannot support sql as follow:
> {code:java}
> select * from emp join dept where emp.deptno = dept.deptno{code}
> However in mysql and hive， such sql runs well.Should we support this kind of
> inner join without on-condition？
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