branch-4.0: [fix](fe) Preserve nth_value semantics for reversed window frames #64864#65020
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branch-4.0: [fix](fe) Preserve nth_value semantics for reversed window frames #64864#65020morrySnow wants to merge 1 commit into
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### What problem does this PR solve?
Issue Number: None
Related PR: None
Problem Summary: Nereids reverses order keys and window frames for frames ending with UNBOUNDED FOLLOWING so BE can execute an equivalent supported frame shape. nth_value depends on the position within the frame, so reversing the order without adjusting its offset changes the result. This change lets BE interpret negative nth_value offsets as counting from the end of the frame, and rewrites nth_value's offset to 0 - offset when Nereids applies the reverse-window transformation.
### Release note
None
### Check List (For Author)
- Test: Manual test
- Ran git diff --check for the modified BE and FE files. Did not compile per user request.
- Behavior changed: Yes. nth_value keeps equivalent semantics when the window frame is reversed for execution.
- Does this need documentation: No
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Cherry-pick of #64864 to branch-4.0.
#64864 - Preserve nth_value semantics for reversed window frames
Preserve nth_value semantics for reversed window frames by properly negating the offset argument and handling the reversed frame evaluation.
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