Re: [I] Optimize SortPreservingMergeStream for single-column merge [datafusion]

["alan910127 (via GitHub)" <gi...@apache.org>]

alan910127 commented on issue #13642:
URL: https://github.com/apache/datafusion/issues/13642#issuecomment-2632903421

   I've found that the sort isn't actually planned as a single-column sort. The `expressions` in this case contains multiple columns:
   
   ```rust
   // SQL: row_number() over (partition by id6 order by v3 desc)
   LexOrdering { 
       inner: [
           PhysicalSortExpr {
               expr: Column { name: "id6", index: 0 },
               options: SortOptions { descending: false, nulls_first: false }
           },
           PhysicalSortExpr {
               expr: Column { name: "v3", index: 1 }, 
               options: SortOptions { descending: true, nulls_first: true }
           }
       ]
   }
   ```
   
   I'm not sure whether this behavior is expected or if the plan should have used a single-column sort optimization in this case.


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