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https://issues.apache.org/jira/browse/CALCITE-4170?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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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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