branch-4.1: [improvement](fe) Enhance COALESCE simplification to remove all NullLiterals #62266#62808
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yiguolei merged 1 commit intobranch-4.1from Apr 25, 2026
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…iterals (#62266) The existing COALESCE simplification rule in SimplifyConditionalFunction only removed leading NullLiteral arguments. When a nullable non-NullLiteral argument was encountered, all remaining arguments (including trailing/interleaved NullLiterals) were preserved. Additionally, an early exit prevented any simplification when the first argument was a nullable non-NullLiteral. For example, `coalesce(null, null, ..., null, i1, null)` was simplified to `coalesce(i1, null)` instead of just `i1`. The improved algorithm: 1. Skips ALL NullLiteral arguments (not just leading ones) 2. Truncates at the first non-nullable argument (subsequent args are unreachable) 3. Returns the single remaining expression directly when only one is left ### Release note Improved COALESCE expression simplification to remove all NULL literal arguments and truncate unreachable arguments after the first non-nullable expression. ### Check List (For Author) - Test: Unit Test - Behavior changed: No - Does this need documentation: No Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
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Cherry-picked from #62266