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https://issues.apache.org/jira/browse/CALCITE-4990?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17482285#comment-17482285
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yanjing.wang commented on CALCITE-4990:
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I have a draft version on
[branch|https://github.com/hannerwang/calcite/tree/union_all_fusion_to_single]
,Welcome review, and any suggestions will be appreciated.
> Add SetOpFilterMergeRule for Converting UNION with same inputs but different
> filters to single input with OR Filter
> -------------------------------------------------------------------------------------------------------------------
>
> Key: CALCITE-4990
> URL: https://issues.apache.org/jira/browse/CALCITE-4990
> Project: Calcite
> Issue Type: Wish
> Components: core
> Affects Versions: 1.29.0
> Reporter: yanjing.wang
> Assignee: yanjing.wang
> Priority: Major
> Fix For: 1.30.0
>
> Attachments: UnionAllToOr.png
>
>
> The attached diagram illustrates how the new rule works.
> !UnionAllToOr.png!
> The rule will be useful when Input Sub Tree is a computing-intensive or large
> IO operation,
> and it works for N-way Union, not just 2-way Union. In addition, The Project
> operator will be optional present.
>
> It has some prerequisites when applying the rule to rel.
> 1. Project and Input Sub Tree must be identical.
> 2. For UNION:
> New Filter = left Filter OR right Filter.
> For UNION ALL:
> left Filter, right Filter must have no overlap.
>
> Example:
> {code:java}
> SELECT a, b FROM t WHERE c = 1
> UNION ALL
> SELECT a, b FROM t WHERE c = 2
> UNION ALL
> SELECT a, b FROM t WHERE c = 3 {code}
> After applying the rule, we get
> {code:java}
> SELECT a, b FROM t WHERE c in (1, 2, 3) {code}
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