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https://issues.apache.org/jira/browse/CALCITE-2041?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16254378#comment-16254378
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Julian Hyde commented on CALCITE-2041:
--------------------------------------
Nullability can only change in one direction, so let's be specific: a1 has a
nullable type, and a2 is a not-null value.
Potentially this could cause the whole expression to change type from nullable
to not null. So if the type of the whole expression needs to be preserved
(think project expressions) compensating casts will need to be added at the
top.
> Adding the ability to turn off nullability matching for ReduceExpressionsRule
> -----------------------------------------------------------------------------
>
> Key: CALCITE-2041
> URL: https://issues.apache.org/jira/browse/CALCITE-2041
> Project: Calcite
> Issue Type: Bug
> Reporter: slim bouguerra
> Assignee: Julian Hyde
> Fix For: 1.15.0
>
>
> In some cases, the user needs to select whether or not to add casts that
> match nullability.
> One of the motivations behind this is to avoid unnecessary casts like the
> following example.
> original filter
> {code}
> OR(AND(>=($0, CAST(_UTF-16LE'2010-01-01 00:00:00
> UTC'):TIMESTAMP_WITH_LOCAL_TIME_ZONE(15)), <=($0, CAST(_UTF-16LE'2012-03-01
> 00:00:00 UTC'):TIMESTAMP_WITH_LOCAL_TIME_ZONE(15))))
> {code}
> the optimized expression with matching nullability
> {code}
> OR(AND(CAST(>=($0, 2010-01-01 00:00:00)):BOOLEAN, CAST(<=($0, 2012-03-01
> 00:00:00)):BOOLEAN))
> {code}
> As you can see this extra cast gets into the way of following plan
> optimization steps.
> The desired expression can be obtained by turning off the nullability
> matching.
> {code}
> OR(AND(>=($0, 2010-01-01 00:00:00), <=($0, 2012-03-01 00:00:00)))
> {code}
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