Details
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New Feature
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Status: Open
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Minor
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Resolution: Unresolved
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None
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None
Description
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.
Attachments
Issue Links
- is related to
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CALCITE-794 Detect cycles when computing statistics
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- Closed
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CALCITE-3890 Derive IS NOT NULL filter for the inputs of inner join
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- Closed
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- Closed
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- links to