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Posted to issues@calcite.apache.org by "Julian Hyde (Jira)" <ji...@apache.org> on 2020/08/09 22:40:00 UTC
[jira] [Updated] (CALCITE-4170) Improve simplification of "<>"
predicates
[ https://issues.apache.org/jira/browse/CALCITE-4170?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]
Julian Hyde updated CALCITE-4170:
---------------------------------
Description:
Improve simplification of "<>" (not equals) predicates. The goal is to simplify "a <> 1 or a = 1" to "true".
Today we can simplify "a = 1 or a <> 1" to "true" (the same expression with the terms re-ordered) but we cannot simplify "a <> 1 or a = 1" to "true". The problem is this. The algorithm for simplifying "or" builds a up a list of predicates as it works left to right. After dealing with "a = 1" RexSimplifier has a predicate "a = 1" and therefore it can simplify the next predicate to anything that returns the right result over the possible inputs - which will not include a = 1 - and therefore 'a <> 1' can be simplified to 'true'.
But today, we can't take that approach with "a <> 1 or a = 1" because "a <> 1" cannot be represented as a single range. It needs two ranges - less than 1 or greater than 1. The fix is therefore to allow predicates to be range sets not just ranges.
was:
Improve simplification of "<>" (not equals) predicates.
Today we can simplify "a = 1 or a <> 1" to "true" but we cannot simplify "a <> 1 or a = 1" to "true". The problem is this. The algorithm for simplifying "or" builds a up a list of predicates as it works left to right. After dealing with "a = 1" RexSimplifier has a predicate "a = 1" and therefore it can simplify the next predicate to anything that returns the right result over the possible inputs - which will not include a = 1 - and therefore 'a <> 1' can be simplified to 'true'.
But today, we can't take that approach with "a <> 1 or a = 1" because "a <> 1" cannot be represented as a single range. It needs two ranges - less than 1 or greater than 1. The fix is therefore to allow predicates to be range sets not just ranges.
> Improve simplification of "<>" predicates
> -----------------------------------------
>
> Key: CALCITE-4170
> URL: https://issues.apache.org/jira/browse/CALCITE-4170
> Project: Calcite
> Issue Type: Bug
> Reporter: Julian Hyde
> Priority: Major
>
> Improve simplification of "<>" (not equals) predicates. The goal is to simplify "a <> 1 or a = 1" to "true".
> Today we can simplify "a = 1 or a <> 1" to "true" (the same expression with the terms re-ordered) but we cannot simplify "a <> 1 or a = 1" to "true". The problem is this. The algorithm for simplifying "or" builds a up a list of predicates as it works left to right. After dealing with "a = 1" RexSimplifier has a predicate "a = 1" and therefore it can simplify the next predicate to anything that returns the right result over the possible inputs - which will not include a = 1 - and therefore 'a <> 1' can be simplified to 'true'.
> But today, we can't take that approach with "a <> 1 or a = 1" because "a <> 1" cannot be represented as a single range. It needs two ranges - less than 1 or greater than 1. The fix is therefore to allow predicates to be range sets not just ranges.
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