[
https://issues.apache.org/jira/browse/CALCITE-3969?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17100281#comment-17100281
]
Haisheng Yuan commented on CALCITE-3969:
----------------------------------------
I don't think there is a need for \{{RelTrait.canApply(TargetMapping)}}. e.g.
RelCollation, the result is either another collation or not sorted anymore.
> Method RelTrait.apply(Mappings.Mapping) throws exception when mapping doesn't
> cover collation or distribution keys
> ------------------------------------------------------------------------------------------------------------------
>
> Key: CALCITE-3969
> URL: https://issues.apache.org/jira/browse/CALCITE-3969
> Project: Calcite
> Issue Type: Bug
> Components: core
> Reporter: Roman Kondakov
> Assignee: Roman Kondakov
> Priority: Major
> Labels: pull-request-available
> Fix For: 1.23.0
>
> Time Spent: 1h 20m
> Remaining Estimate: 0h
>
> Let's consider we have an input {{(id, name)}} ordered by {{id}} (i.e.
> collation == {{[0]}}). If we have a {{Project("name")}} on the top of this
> input and we apply project's mapping on the collation, we'll end up with
> exception:
> {noformat}
> java.lang.NullPointerException: at index 0
> at
> com.google.common.collect.ObjectArrays.checkElementNotNull(ObjectArrays.java:239)
> at
> com.google.common.collect.ObjectArrays.checkElementsNotNull(ObjectArrays.java:230)
> at
> com.google.common.collect.ObjectArrays.checkElementsNotNull(ObjectArrays.java:225)
> at
> com.google.common.collect.ImmutableList.construct(ImmutableList.java:281)
> at
> com.google.common.collect.ImmutableList.copyOf(ImmutableList.java:239)
> at org.apache.calcite.rel.RelCollations.of(RelCollations.java:69)
> at org.apache.calcite.rex.RexUtil.apply(RexUtil.java:1271)
> at
> org.apache.calcite.rel.RelCollationImpl.apply(RelCollationImpl.java:122)
> at
> org.apache.calcite.rel.RelCollationImpl.apply(RelCollationImpl.java:40)
> {noformat}
> This happens because the collation field {{id}} is not a part of the mapping.
> The same problem is with distribution trait when distribution keys are not
> covered by the mapping.
> Calcite should handle such situations gracefully. If it is not possible to
> deduce the collation/distribution after the mapping application, we should
> return:
> * {{EMPTY}} collation for {{RelCollation}} trait.
> * {{RANDOM_DISTRIBUTED}} distribution for {{RelDistribution}} trait.
--
This message was sent by Atlassian Jira
(v8.3.4#803005)
