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https://issues.apache.org/jira/browse/CALCITE-4559?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17324840#comment-17324840
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Vladimir Ozerov commented on CALCITE-4559:
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[~julianhyde] [~hyuan], I propose to treat my comment about the rule order as a
rough idea, not a call to action. For example, image that we have a predicate
{code}
x IN (a,b)
{code}
We may want to apply the rule to convert it to {{OR}}, and then apply more
simplification rules on the produced nodes. E.g.:
{code}
Rule 1: x IN (a,b) -> x=a OR x=b
Rule 2: x=a OR x=b -> x=a (because we know from the metadata that x is never
equal to b)
{code}
I agree, that the current approach already allows us to do that - just call two
{{RexRulePrograms}} one by one. However, the alternative strategies might be
more efficient implementation-wise. For example, the may possibly produce less
garbage. All in all, I do not think this is important at the moment.
> Create 'interface RexRule', a modular rewrite for row-expressions
> -----------------------------------------------------------------
>
> Key: CALCITE-4559
> URL: https://issues.apache.org/jira/browse/CALCITE-4559
> Project: Calcite
> Issue Type: Bug
> Reporter: Julian Hyde
> Assignee: Julian Hyde
> Priority: Major
>
> We propose to add {{class RexRule}}, a rewrite rule for row-expressions
> ({{class RexNode}}).
> {{class RexRule}} is analogous to how {{class RelRule}} (and the older
> {{class RelOptRule}}) operates on relational expressions ({{interface
> RelNode}}). Also, {{class RexRuleProgram}} is analogous to {{HepProgram}} and
> {{VolcanoPlanner}} (it indexes rules so that we do not have to try every rule
> against every part of the expression). And a rule describes which operands it
> matches using {{RexRule.describe(RexRule.OperandBuilder)}}, similar to
> calling {{RelRule.Config.operandSupplier().apply()}}.
> The advantages of {{RexRule}} are similar to {{RelRule}}: rules can be
> defined in a modular way, can be documented and tested individually, and can
> be enabled individually.
> The rules could be applied in various ways. {{RelBuilder.Config}} could
> contain a {{RexRuleProgram}} that would be applied every time an expression
> is simplified by a {{RelBuilder}}. There could also be a sub-class of
> {{interface RelShuttle}} that applies the rules to every {{RexNode}} in a
> tree (e.g. inside {{Filter}}, {{Project}} and {{Join}}).
> I don't yet know whether, or how, rules might support 3-valued boolean logic
> ({{RexUnknownAs}}). For example, a rule that simplifies "x = x" to "TRUE" is
> valid in an "unknownAsFalse" context (e.g. as top-level of {{Filter}}
> condition), but not in an "unknownAsUnknown" context (e.g. in {{Project}}
> expression).
> This case is related to CALCITE-3470 (making relational and row-expression
> rules more similar, as in CockroachDB), but would deliver an API rather than
> a textual DSL.
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