[CALCITE-4170] Improve simplification of "<>" predicates

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 1.26.0
• Assignee: Unassigned
• Reporter: Julian Hyde
• Created: 09/Aug/20 22:37
• Updated: 06/Oct/20 17:16
• Resolved: 21/Aug/20 06:35

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.

Issue Links

• is related to: CALCITE-3852 RexSimplify doesn't simplify NOT EQUAL predicates