Julian Hyde created CALCITE-4170:
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Summary: Improve simplification of "<>" predicates
Key: CALCITE-4170
URL: https://issues.apache.org/jira/browse/CALCITE-4170
Project: Calcite
Issue Type: Bug
Reporter: Julian Hyde
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.
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