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https://issues.apache.org/jira/browse/CALCITE-4215?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17189748#comment-17189748
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Vladimir Sitnikov commented on CALCITE-4215:
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In other words: I understand how "unknown collation" differs from "known empty
collation", however, I think that distinction won't improve our planning, and
features like "allow collation to be null" would make the code significantly
harder to maintain.
> Ensure org.apache.calcite.schema.Statistic uses null vs emptyList
> appropriately
> -------------------------------------------------------------------------------
>
> Key: CALCITE-4215
> URL: https://issues.apache.org/jira/browse/CALCITE-4215
> Project: Calcite
> Issue Type: Sub-task
> Components: core
> Affects Versions: 1.25.0
> Reporter: Vladimir Sitnikov
> Priority: Major
> Labels: pull-request-available
> Time Spent: 10m
> Remaining Estimate: 0h
>
> null: statistic is *not* *known*
> emptyList: statistic is *known*, and the value is *empty* (e.g. no unique
> keys in the table)
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