branch-4.1: [fix](be) Fix nth_value for upper bounded windows #64864#64896
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### What problem does this PR solve? Related PR: #50559 Problem Summary: nth_value over an upper-bounded/lower-unbounded window frame such as ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING is normalized by reversing the order and frame, then evaluating nth_value with a negative offset over a cumulative frame. The BE nth_value window state replaced the tracked frame row count on each range update, so later rows in the cumulative frame could address the wrong row or return NULL. The fix keeps the cumulative frame row count across range updates, and FE preserves literal offset typing when negating bigint nth_value arguments. This adds BE unit coverage for the reversed cumulative execution path and a regression case comparing nth_value to lead for the original SQL frame. ### Release note Fix nth_value results for ROWS BETWEEN CURRENT ROW AND UNBOUNDED FOLLOWING window frames.
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FE UT Coverage ReportIncrement line coverage |
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BE Regression && UT Coverage ReportIncrement line coverage Increment coverage report
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yiguolei
approved these changes
Jun 26, 2026
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Cherry-picked from #64864