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https://issues.apache.org/jira/browse/CALCITE-3198?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16885475#comment-16885475
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Julian Hyde commented on CALCITE-3198:
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{{ReduceExpressionsRule}} is about constant reduction (aided by predicates). Is
constant reduction the best framing for this optimization? (It might be, I
haven't thought it through.) Simplification (as in {{RexSimplify}}, and
automatically applied by {{RelBuilder.filter}} and other methods) is an
alternative framing to consider.
> ReduceExpressionsRule.FILTER_INSTANCE does not reduce 'NOT(x=a AND x=b)'
> ------------------------------------------------------------------------
>
> Key: CALCITE-3198
> URL: https://issues.apache.org/jira/browse/CALCITE-3198
> Project: Calcite
> Issue Type: Bug
> Affects Versions: 1.20.0
> Reporter: Ruben Quesada Lopez
> Priority: Minor
>
> Currently, ReduceExpressionsRule.FILTER_INSTANCE can successfully reduce a
> query like this one (see RelOptRulesTest#testReduceConstantsDup):
> {code}
> // query:
> select d.deptno from dept d where d.deptno=7 and d.deptno=8
> // plan before:
> LogicalProject(DEPTNO=[$0])
> LogicalFilter(condition=[AND(=($0, 7), =($0, 8))])
> LogicalTableScan(table=[[CATALOG, SALES, DEPT]])
> // plan after:
> LogicalProject(DEPTNO=[$0])
> LogicalValues(tuples=[[]])
> {code}
> As we can see, since the filter is 'always false', the
> LogicalTableScan+LogicalFilter are correctly replaced by an empty
> LogicalValues.
> However, the same filter with a NOT expression, is not correctly simplified:
> {code}
> // query:
> select d.deptno from dept d where not(d.deptno=7 and d.deptno=8)
> // plan before:
> LogicalProject(DEPTNO=[$0])
> LogicalFilter(condition=[NOT(AND(=($0, 7), =($0, 8)))])
> LogicalTableScan(table=[[CATALOG, SALES, DEPT]])
> // plan after (actual, NOT distributivity for AND):
> LogicalProject(DEPTNO=[$0])
> LogicalFilter(condition=[OR(<>($0, 7), <>($0, 8))])
> LogicalTableScan(table=[[CATALOG, SALES, DEPT]])
> // plan after (expected, filter removed):
> LogicalProject(DEPTNO=[$0])
> LogicalTableScan(table=[[CATALOG, SALES, DEPT]])
> {code}
> Since the filter is the negated of an 'always false filter' (the one used in
> the previous query), it is therefore an 'always true filter', so the expected
> behavior is that the LogicalFilter should be removed, and it is not.
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