[GitHub] [arrow-datafusion] mustafasrepo commented on a diff in pull request #5772: Change required input ordering API

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

mustafasrepo commented on code in PR #5772:
URL: https://github.com/apache/arrow-datafusion/pull/5772#discussion_r1151727666


##########
datafusion/core/src/physical_plan/windows/mod.rs:
##########
@@ -187,6 +188,30 @@ fn create_built_in_window_expr(
     })
 }
 
+pub(crate) fn calc_requirements(
+    partition_by_exprs: &[Arc<dyn PhysicalExpr>],
+    orderby_sort_exprs: &[PhysicalSortExpr],
+) -> Option<Vec<PhysicalSortRequirement>> {
+    let mut sort_reqs = vec![];
+    for partition_by in partition_by_exprs {
+        sort_reqs.push(PhysicalSortRequirement {
+            expr: partition_by.clone(),
+            options: None,
+        });
+    }
+    for PhysicalSortExpr { expr, options } in orderby_sort_exprs {
+        let contains = sort_reqs.iter().any(|e| expr.eq(&e.expr));
+        if !contains {
+            sort_reqs.push(PhysicalSortRequirement {
+                expr: expr.clone(),
+                options: Some(*options),
+            });
+        }
+    }
+    // Convert empty result to None. Otherwise wrap result inside Some()
+    (!sort_reqs.is_empty()).then_some(sort_reqs)
+}
+

Review Comment:
   In the case of `PARTITION BY a, ORDER BY a`. We do not add requirement for column `a`. The reason is that all partition would consist of the same value of `a`. Hence `ORDER BY` doesn't really define a direction(all `a` values would be same.). Above operation can produce correct result when its input is ordered according `a ASC` or `a DESC`. 



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