branch-4.1: [fix](nereids) Allocate fresh ExprId for constants when pushing project into Union #62296#63018
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…ct into Union (#62296) ### What problem does this PR solve? Issue Number: close #62294 Problem Summary: When `PushProjectIntoUnion` folds a parent `Project`'s expression into a `LogicalUnion`'s `constantExprsList`, the outer `Alias` of a non-`SlotReference` project expression is preserved by `ExpressionUtils.replaceNameExpression`. Its `ExprId` then collides with the new UNION output `ExprId` (which comes from the parent project's output `Alias`) and is reused across every constant row of the same column. Downstream rules such as `PushDownFilterThroughSetOperation` rely on the invariant that each `constantExprsList` row carries `NamedExpression`s whose `ExprId`s are distinct from the UNION output and from each other across rows; the collision causes them to mis-rewrite the plan and return wrong results, e.g. ```sql WITH tbl0(n) AS (SELECT 1 UNION ALL SELECT 3 UNION ALL SELECT NULL), tbl1(n) AS (SELECT 2 UNION ALL SELECT NULL UNION ALL SELECT 1) SELECT (n*2) AS n FROM tbl0 INTERSECT SELECT (n*2) AS n FROM tbl1; ``` `PushProjectThroughUnion` has the same class of bug in its mixed-union constant-row branch: when `MergeOneRowRelationIntoUnion` folds a `LogicalOneRowRelation` into the union's `constantExprsList`, an outer `Alias(Cast(slot))` project survives `outerProject.rewriteUp` with its parent `ExprId` intact, and then the same `ExprId` is reused as the new UNION output via `project.toSlot()`. The plan-level invariant is broken even though no current downstream rule appears to mis-handle the specific shape today. Fix: - `PushProjectIntoUnion`: after folding the substituted expression, re-wrap the result in a fresh `Alias` so each constant cell receives a new unique `ExprId`. Qualifier and name from the folded `Alias` are preserved. The `SlotReference` branch is left unchanged because it already returns the original `NamedExpression` from `constExprs` whose `ExprId`s are row-distinct and not equal to the UNION output `ExprId`. - `PushProjectThroughUnion`: same treatment for the constant-row non-Slot branch — re-wrap the rewritten `Alias` to allocate a fresh `ExprId`. Introduced by #39450 (closest commit touching the relevant lines; the file `PushProjectIntoUnion` was originally added by #27947). ### Release note Fix wrong results for INTERSECT/EXCEPT/UNION over constant rows when the projection contains expressions such as `((col*2) AS col)`, and harden the parallel `PushProjectThroughUnion` rule against the same class of ExprId collision. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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yiguolei
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May 7, 2026
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Cherry-picked from #62296