ruanhui created CALCITE-6363:
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Summary: 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
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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