FWIW I use an implementation of that idea locally and did a few
end-to-end tests and it seems to work so far.
I can prepare a PR so we can discuss this if you tell me an issue number
or that I should create one for this.
Mit freundlichen Grüßen,
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*Christian Beikov*
Am 24.08.2017 um 02:13 schrieb Julian Hyde:
Jesus,
Can you answer this question for Christian please? Seems like a reasonable use
case, and your area of expertise.
Julian
On Aug 20, 2017, at 12:25 PM, Christian Beikov <[email protected]>
wrote:
I just discovered that queries containing left joins aren't rewritten when
materializations are available and wondered why that is a limitation. I looked
a bit into the implementation and found out that
org.apache.calcite.rel.metadata.RelMdAllPredicates#getAllPredicates(org.apache.calcite.rel.core.Join,
org.apache.calcite.rel.metadata.RelMetadataQuery) returns null when
encountering a non-inner join.
For an inner join, the method returns essentially the join predicate, so I thought a left
join should be similar. How about returning an OR node that asserts input refs of
"outer-joined" tables are null if unmatched?
Let's consider an example query like "from emp e left join dept d on e.deptno =
d.deptno"
If the join were an inner join, the return would be "=(e.deptno, d.deptno)". In case of a
left join I'd suppose it returns "OR(IS_NULL(d.deptno),=(e.deptno, d.deptno))". Would
that be sufficient to implement left join support or do you have something different in mind? I
couldn't find a ticket for that particular case to discuss a possible implementation so please
direct me if you already tracked that issue.
--
Mit freundlichen Grüßen,
------------------------------------------------------------------------
*Christian Beikov*
