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https://issues.apache.org/jira/browse/CALCITE-987?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15025097#comment-15025097
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Julian Hyde commented on CALCITE-987:
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Now regarding {{limit 0}} specifically. We knew it was a shortcut when we used
*estimated* row count to avoid pushing limit twice. I like the idea that the
estimated row count should never be less than one -- it seems appropriate for
the vast majority of the things people use estimated row count for.
I think we should add a new kind of metadata, maximum row count. Use that,
rather than estimated row count, to make sure that we don't push limit twice.
> Push limit 0 will result in an infinite loop
> --------------------------------------------
>
> Key: CALCITE-987
> URL: https://issues.apache.org/jira/browse/CALCITE-987
> Project: Calcite
> Issue Type: Bug
> Reporter: Pengcheng Xiong
> Assignee: Pengcheng Xiong
> Attachments: CALCITE-987.01.patch
>
>
> We use "checkInputForCollationAndLimit" in RelMdUtil.java to check the input
> #rows. However, it calls RelMetadataQuery.getRowCount which will validate the
> #rows. The validation will change #row=0 to #row=1. This will result in an
> infinite loop to push limit. The affected rules include
> SortUnionTransposeRule and any Sort***TransposeRules that call
> checkInputForCollationAndLimit.
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