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https://issues.apache.org/jira/browse/CALCITE-2247?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16483390#comment-16483390
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Julian Hyde commented on CALCITE-2247:
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I was thinking along similar lines. We could pass an "interpretation" function.
In your example the interpretation function maps true → true, unknown
→ false, false → true and is commonly called IS NOT UNKNOWN.
There are 27 (3^3) functions that map (false, unknown, true) to (false,
unknown, true). Here are the most interesting 11:
||false ||unknown ||true ||Name
|false |unknown |true |identity
|true |unknown |false |NOT
|false |false |true |IS TRUE
|true |true |false |IS NOT TRUE
|true |false |false |IS FALSE
|false |true |true |IS NOT FALSE
|false |true |false |IS UNKNOWN
|true |false |true |IS NOT UNKNOWN
|false |false |false |FALSE
|unknown |unknown |unknown |UNKNOWN
|true |true |true |TRUE
For the purposes of simplification, I think that 3 cover the main cases without
making the code too complicated:
* IS TRUE (unknown-as-false) is used when a predicate occurs in WHERE, ON or
HAVING;
* IS NOT FALSE (unknown-as-true) occurs in NOT and OR;
* Identifier (unknown-as-unknown) occurs when a condition appears in the SELECT
clause, and therefore you want 3-valued logic returned.
> Add rule to push in condition condition into a related disjunctive expression
> -----------------------------------------------------------------------------
>
> Key: CALCITE-2247
> URL: https://issues.apache.org/jira/browse/CALCITE-2247
> Project: Calcite
> Issue Type: Improvement
> Reporter: Zoltan Haindrich
> Assignee: Zoltan Haindrich
> Priority: Major
>
> Simplify expressions like: {code}a = 1 AND (a = 1 OR a = 2){code} to {code}a
> = 1{code}
> Conditions to apply will be:
> * in an AND condition there exists a comparison(c) and an OR (o)
> * o and c only reference 1 variable
> See HIVE-19097 for more info.
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