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https://issues.apache.org/jira/browse/CALCITE-5013?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17514391#comment-17514391
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Jiajun Xie commented on CALCITE-5013:
-------------------------------------
Thank you very much for your guidance. I was confused before that there was no
*SqlOperator* corresponding to LIMIT. From your code, I learned that
*SqlinternalOperators* can create necessary operators.
I cherry pick your commit and add it to
https://github.com/apache/calcite/pull/2724
> JDBC adapter should retain parentheses if a query in a UNION has a LIMIT
> clause
> -------------------------------------------------------------------------------
>
> Key: CALCITE-5013
> URL: https://issues.apache.org/jira/browse/CALCITE-5013
> Project: Calcite
> Issue Type: Bug
> Components: core
> Reporter: Jiajun Xie
> Priority: Major
>
> The JDBC adapter, when generating SQL, should retain parentheses if one of
> the inputs to a set operator (e.g. UNION) has an LIMIT clause.
> In standard SQL, the operand of UNION should not have LIMIT or ORDER BY. So
> parse will fail in {{SqlParserTetest#testLimitUnion}} and
> {{SqlParserTetest#OrderUnion}}.
> When users use parentheses, most engines allow it. See the discussion:
> CALCITE-1892.
> For simple example, parentheses control the scope of the limit
> {code:java}
> select "product_id" from "product"
> union all
> (select "product_id" from "product" limit 10){code}
> {{unparseBinarySyntax}} will miss parentheses, this change will affect
> semantics
> {code:java}
> SELECT \"product_id\" FROM \"foodmart\".\"product\"
> UNION ALL
> SELECT \"product_id\" FROM \"foodmart\".\"product\"
> FETCH NEXT 10 ROWS ONLY -- Affect semantics{code}
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