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https://issues.apache.org/jira/browse/CALCITE-6357?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17836338#comment-17836338
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Julian Hyde commented on CALCITE-6357:
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We added {{RelRoot}} way back in CALCITE-819 to express the fact that you want
columns to have particular names, and that you want the relation to be sorted
by columns that are not returned in the result.
If you need that, use {{RelRoot}}. But it is not a {{RelNode}} because adding
those capabilities to {{RelNode}} would hamper the operations of the planner.
> Calcite enforces select arguments count to be same as row schema fields which
> causes aliases to be ignored
> ----------------------------------------------------------------------------------------------------------
>
> Key: CALCITE-6357
> URL: https://issues.apache.org/jira/browse/CALCITE-6357
> Project: Calcite
> Issue Type: Bug
> Reporter: Brachi Packter
> Priority: Major
>
> Calcite RelBuilder.ProjectNamed checks if row size in the select is identical
> to schema fields, if no, it creates a project with fields as they appear in
> the select , meaning if they have aliases, they are returning with their
> aliases.
> Here, it checks if they are identical:
> https://github.com/apache/calcite/blob/f14cf4c32b9079984a988bbad40230aa6a59b127/core/src/main/java/org/apache/calcite/tools/RelBuilder.java#L2063
> using RexUtil.isIdentity method:
> ```
> public static boolean isIdentity(List<? extends RexNode> exps,
> RelDataType inputRowType) {
> return inputRowType.getFieldCount() == exps.size()
> && containIdentity(exps, inputRowType, Litmus.IGNORE);
> }
> ```
> This is the problematic part `inputRowType.getFieldCount() == exps.size()`
> If they are identical, and return with their aliases, it is ignored in the
> "rename" method later on
> https://github.com/apache/calcite/blob/f14cf4c32b9079984a988bbad40230aa6a59b127/core/src/main/java/org/apache/calcite/tools/RelBuilder.java#L2125
> and alias is skipped
> https://github.com/apache/calcite/blob/f14cf4c32b9079984a988bbad40230aa6a59b127/core/src/main/java/org/apache/calcite/tools/RelBuilder.java#L2137
> This doesn't impact calcite queries, but in Apache Beam they are doing some
> optimization on top of it,
> https://github.com/apache/beam/blob/master/sdks/java/extensions/sql/src/main/java/org/apache/beam/sdk/extensions/sql/impl/rule/BeamAggregateProjectMergeRule.java
> which causes aliases to be ignored, and data is returning suddenly without
> correct column field.
> I believe the isIdentity check can causes more issues if not fixed, we need
> to understand why is it enforced? isn't it valid to have different size of
> fields in select from what we have in the schema?
> In our case we have a one big row and we run on it different queries, each
> with different fields in the select.
> Beam issue
> https://github.com/apache/beam/issues/30498
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