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https://issues.apache.org/jira/browse/CALCITE-2675?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16688318#comment-16688318
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Zoltan Haindrich commented on CALCITE-2675:
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My proposed solution is to remove the invocation of simplification after every
replacements
[ReduceExpression|https://github.com/apache/calcite/blob/fcc8bf7f44f92efb3c9a1e1f51ffc1a09cab27b9/core/src/main/java/org/apache/calcite/rel/rules/ReduceExpressionsRule.java#L794]
may make...because in the end ReduceExpression will make a final pass on the
expression with the
[simplifier|https://github.com/apache/calcite/blob/fcc8bf7f44f92efb3c9a1e1f51ffc1a09cab27b9/core/src/main/java/org/apache/calcite/rel/rules/ReduceExpressionsRule.java#L549]
- which is already capable of [wrapping expression into cast armor to protect
against nullability
changes|https://github.com/apache/calcite/blob/fcc8bf7f44f92efb3c9a1e1f51ffc1a09cab27b9/core/src/main/java/org/apache/calcite/rex/RexUtil.java#L2657]
Notes:
* HepRuleCall checks for type [equivavalence|
https://github.com/apache/calcite/blob/fcc8bf7f44f92efb3c9a1e1f51ffc1a09cab27b9/core/src/main/java/org/apache/calcite/plan/hep/HepRuleCall.java#L57];
I think narrowing the nullability should be allowed - I think it might also
help other parts
* unfortunately RelBuilder may "cover up" for this bug in some cases - by
simplifying earlier…(I think calling simplify during tree building is a little
bit too greedy - I think that the optimizer should be the one doing all the
optimization)
> ReduceExpressionRule may leave behind altered types w.r.t nullability
> ---------------------------------------------------------------------
>
> Key: CALCITE-2675
> URL: https://issues.apache.org/jira/browse/CALCITE-2675
> Project: Calcite
> Issue Type: Bug
> Reporter: Zoltan Haindrich
> Assignee: Zoltan Haindrich
> Priority: Major
>
> If a simplification could happen after some [ReduceExpression
> rewrite|https://github.com/apache/calcite/blob/fcc8bf7f44f92efb3c9a1e1f51ffc1a09cab27b9/core/src/main/java/org/apache/calcite/rel/rules/ReduceExpressionsRule.java#L794];
> the simplification result may have a slightly different type in nullability.
> {code}
> @Test public <T> void testReduceCaseNullabilityChange() throws Exception {
> HepProgram program = new HepProgramBuilder()
> .addRuleInstance(ReduceExpressionsRule.FILTER_INSTANCE)
> .addRuleInstance(ReduceExpressionsRule.PROJECT_INSTANCE)
> .build();
> try (Hook.Closeable a =
> Hook.REL_BUILDER_SIMPLIFY.add(Hook.propertyJ(false))) {
> checkPlanning(program,
> "select case when empno = 1 then 1 when 1 IS NOT NULL then 2 else
> null end as qx "
> + "from emp");
> }
> {code}
> Exposed by CALCITE-1413 changes; I'm not sure if there is any other
> variations for which the same could happen.
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