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https://issues.apache.org/jira/browse/CALCITE-2102?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16298686#comment-16298686
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Julian Hyde commented on CALCITE-2102:
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It should not throw. It is valid SQL.
Remember, when you write {{ORDER BY x, y}} you are saying to use {{y}} as a
tie-break when two rows have the same {{x}} value. If you provide a useless
expression for {{y}} it's silly but it's still valid SQL.
> SqlToRelConverter (or perhaps RelBuilder) ignore repeat sort keys. In
> addition, it should also prevent the incompatible sort keys.
> ----------------------------------------------------------------------------------------------------------------------------------
>
> Key: CALCITE-2102
> URL: https://issues.apache.org/jira/browse/CALCITE-2102
> Project: Calcite
> Issue Type: Bug
> Reporter: John Fang
> Assignee: Julian Hyde
>
> I test the query {{SELECT a, c FROM MyTable ORDER BY a DESC, a
> DESC}}. And the collation of LogicalSort is {{[0 DESC, 0 DESC]}} , thus it
> will order by the repeater fields. I think the calcite should removal the
> repeated fields, thus it make the LogicalSort whose collation is {{[0 DESC]}}
> be more reasonable.
> Considering compatibility，it may be better make {{SqlToRelConverter}}
> (or perhaps RelBuilder) ignore sort keys that have appeared earlier in the
> key. In addition, it should also prevent the incompatible sort keys. It
> should throw illegalargumentexception for the query {{SELECT a, c FROM
> MyTable ORDER BY a DESC, a ASC}} because of the incompatibility.
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