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branch-4.1: [fix](rbo) Preserve union constant rows across rewrites #67790 - #68172
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## Problem A UNION ALL could lose constant rows when a later rewrite exposed another one-row child. Queries that combine an existing constant branch with a single-row GROUP BY or DISTINCT branch returned only the newly exposed row. ## Root cause MergeOneRowRelationIntoUnion rebuilt the union constant-expression list from only the current children. If an earlier rewrite pass had already moved a constant child into the union metadata, a later pass replaced that metadata instead of retaining it. ## Reproduction ```sql SELECT 1 AS c UNION ALL SELECT c FROM (SELECT 2 AS c) s GROUP BY c; ``` The result incorrectly omitted the row containing 1. The same behavior occurred with DISTINCT and with the branches reversed. ## Fix Seed the rebuilt constant-expression list with the union existing constant rows before appending newly converted one-row children. This preserves row multiplicity across repeated rewrite passes. Add a focused rewrite unit test and named regression queries with runner-generated golden output for GROUP BY, DISTINCT, reversed branch order, and duplicate constant rows. ## Tests - `SetOperationOutputMappingTest`: 4 tests passed - `merge_one_row_relation_into_union`: named golden regression passed in both force-generation and normal comparison modes - Full FE build with UI disabled: passed - Checkstyle: passed
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Thank you for your contribution to Apache Doris. Please clearly describe your PR:
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run buildall |
yiguolei
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Sep 19, 2026
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PR approved by anyone and no changes requested. |
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PR approved by at least one committer and no changes requested. |
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Cherry-picked from #67790