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https://issues.apache.org/jira/browse/CALCITE-6363?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17837714#comment-17837714
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ruanhui commented on CALCITE-6363:
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Thanks for your attention [~jamesstarr] and [~julianhyde] for the quote
{quote}Also, you will need to simplify the pushed down filters after they are
extracted to prevent infinite loops.{quote}
Yes. I use a method arePredicatesEquivalent to determine whether the original
filters and the derived filters are same and if so, we will stop. If you are
interested, you can see my PR for details. I'll appreciate for any feedback.
https://github.com/frostruan/calcite/blob/calcite-6363/core/src/main/java/org/apache/calcite/rel/rules/JoinDeriveEquivalenceFilterRule.java#L123
> Introduce a rule to derive more filters from inner join condition
> -----------------------------------------------------------------
>
> Key: CALCITE-6363
> URL: https://issues.apache.org/jira/browse/CALCITE-6363
> Project: Calcite
> Issue Type: New Feature
> Components: core
> Reporter: ruanhui
> Priority: Minor
> Labels: pull-request-available
>
> Sometimes we can infer more predicates from inner Join , for example, in the
> query
> SELECT * FROM ta INNER JOIN tb ON ta.x = tb.y WHERE ta.x > 10
> we can infer condition tb.y > 10 and we can push it down to the table tb.
> In this way, it is possible to reduce the amount of data involved in the Join.
> To achieve this, here is my idea.
> The core data strucature is two Multimap:
> predicateMap : a map for inputRef to corresponding predicate such as: $1 ->
> [$1 > 10, $1 < 20, $1 = $2]
> equivalenceMap : a map for inputRef to corresponding equivalent values or
> inputRefs such as: $1 -> [$2, 1]
> The filter derivation is divided into 4 steps:
> 1. construct predicate map and equivalence map by traversing all conjunctions
> in the condition
> 2. search map and rewrite predicates with equivalent inputRefs or literals
> 2.1 find all inputRefs that are equivalent to the current inputRef, and then
> rewrite all predicates involving equivalent inputRefs using inputRef, for
> example if we have inputRef $1 = equivInputRef $2, then we can rewrite \{$2 =
> 10} to \{$1 = 10}.
> 2.2 find all predicates involving current inputRef. If any predicate refers
> to another inputRef, rewrite the predicate with the literal/constant
> equivalent to that inputRef, such as: if we have inputRef \{$1 > $2} and \{$2
> = 10} then we can infer new condition \{$1 > 10}.
> 2.3 derive new predicates based on equivalence relation in equivalenceMultimap
> 3. compose all original predicates and derived predicates
> 4. simplify expression such as range merging, like \{$1 > 10 AND $1 > 20} =>
> \{$1 > 20}, \{$1 > $2 AND $1 > $2} => \{$1 > $2}
> Anyone interested in this, please feel free to comment on this issue.
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