[
https://issues.apache.org/jira/browse/CALCITE-1965?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16140440#comment-16140440
]
Christian Beikov commented on CALCITE-1965:
-------------------------------------------
Does it make any sense to have an inner join after an outer join for _simple
equality joins_? By doing that, you essentially force inner join semantics on
the left joins. That's one reason why I only handle plain equality predicates
of outer joins. I haven't thought too much about a possible problematic
scenario yet, but I will certainly try. If you come up with a counter example
before me, please let me know.
It would be very nice if you knew a more general approach to this that might
even allow rewrites in even more cases, I would really love that. I haven't
read the paper nor looked into the matching or rewriting algorithm so I'm not
sure if I am the right person to do anything in there. You seem to already have
an idea about how to tackle that problem :)
Do I understand you correctly, that the changes in {{getAllPredicates}} are ok
or at least that the general idea of pulling up the {{OR(ISNULL(),=())}}
instead of {{=()}} is correct? I'm asking because I'd like to use that method
to determine the predicates of a table that are essential to it's results. When
checking these predicates against change sets, one could determine if a data
change affected the data which is a nice thing to have for materialized views :)
> Support outer joins for materialized views
> ------------------------------------------
>
> Key: CALCITE-1965
> URL: https://issues.apache.org/jira/browse/CALCITE-1965
> Project: Calcite
> Issue Type: Improvement
> Components: core
> Reporter: Christian Beikov
> Assignee: Julian Hyde
>
> Currently, only inner joins are supported for materialized view
> substitutions. The support for outer joins involves creating new pulled up
> predicates in case of outer joins that represent semantics of the join. For a
> join predicate like "a.id = b.id" the inner join just pulls up that
> predicate. When having a left join like e.g. {{select * from a left join b on
> a.id = b.id}}, the actual pulled up predicate would be {{OR(=(a.id,
> b.id),ISNULL(b.id))}}. For a right join it would be {{OR(=(a.id,
> b.id),ISNULL(a.id))}} and for a full outer join it would be {{OR(=(a.id,
> b.id),ISNULL(a.id),ISNULL(b.id))}}
--
This message was sent by Atlassian JIRA
(v6.4.14#64029)
