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https://issues.apache.org/jira/browse/CALCITE-5179?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17548577#comment-17548577
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Steven Talbot commented on CALCITE-5179:
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^^ indeed, in fact in an ideal world UNION ALL would not be a binary operator,
since the nesting required, if you had a very large number of rows in your
values (turned into a union all) could easily blow out the stack trying to
unparse it. Or, you could structure the union operators as a binary tree rather
than the single branching tree. That being said, maybe such a large number
(thousands?) of values is not something we want to overcomplicate the code to
support.
> AssertionError in values with more than two items when
> SqlDialect#supportsAliasedValues is false
> ------------------------------------------------------------------------------------------------
>
> Key: CALCITE-5179
> URL: https://issues.apache.org/jira/browse/CALCITE-5179
> Project: Calcite
> Issue Type: Bug
> Reporter: Steven Talbot
> Assignee: Jiajun Xie
> Priority: Major
> Labels: pull-request-available
> Time Spent: 10m
> Remaining Estimate: 0h
>
> The code at
> [https://github.com/apache/calcite/blob/4b349032c17b95735b12593a65f7027d54d8b8b6/core/src/main/java/org/apache/calcite/rel/rel2sql/RelToSqlConverter.java#L802-L803]
> creates a UNION ALL with an arbitrary number of operands, but [the UNION_ALL
> operator is a
> SqlSetOperator|https://github.com/apache/calcite/blob/4b349032c17b95735b12593a65f7027d54d8b8b6/core/src/main/java/org/apache/calcite/sql/fun/SqlStdOperatorTable.java#L108-L109]
> which is a "SqlBinaryOperator" (Binary syntax). So that generates an
> assertion error when it unparses more than two values at
> [https://github.com/apache/calcite/blob/4b349032c17b95735b12593a65f7027d54d8b8b6/core/src/main/java/org/apache/calcite/sql/SqlUtil.java#L426]
>
> I don't _think_ I've done anything nonstandard, other than use a dialect with
> that flag set to false. To reproduce, create a values RelNode with more than
> two items, convert it with RelToSqlConverter with a dialect using
> supportsAliasedValues() = false (like Redshift), and attempt to unparse the
> resulting SqlNode.
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