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https://issues.apache.org/jira/browse/CALCITE-1498?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15685022#comment-15685022
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Maryann Xue commented on CALCITE-1498:
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[~julianhyde], could you please kindly review this PR for me? Thanks in
advance! https://github.com/apache/calcite/pull/327
> RelMdUtil.checkInputForCollationAndLimit() should also consider input
> collations as a zero-length collation list.
> -----------------------------------------------------------------------------------------------------------------
>
> Key: CALCITE-1498
> URL: https://issues.apache.org/jira/browse/CALCITE-1498
> Project: Calcite
> Issue Type: Bug
> Components: core
> Affects Versions: 1.10.0
> Reporter: Maryann Xue
> Assignee: Maryann Xue
> Priority: Minor
>
> {code}
> // Check if the input is already sorted
> boolean alreadySorted = false;
> if (!alreadySorted) {
> for (RelCollation inputCollation : mq.collations(input)) {
> if (inputCollation.satisfies(collation)) {
> alreadySorted = true;
> break;
> }
> }
> }
> {code}
> if {{mq.collations(input)}} returns an empty array, {{alreadySorted}} will
> always be false even if the required {{collation}} is an empty collation
> (which indicates there's no need to sort).
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