Re: [PR] fix: avoid invalid qualifiers in unparsed subqueries [datafusion]

["blinding-pixels (via GitHub)" <gi...@apache.org>]

blinding-pixels commented on code in PR #24808:
URL: https://github.com/apache/datafusion/pull/24808#discussion_r3901231616


##########
datafusion/sql/src/unparser/plan.rs:
##########
@@ -451,6 +457,92 @@ impl Unparser<'_> {
         }
     }
 
+    /// Return the alias recursion would assign when `plan` must become a
+    /// derived relation below an already rendered projection.
+    fn derived_input_alias(plan: &LogicalPlan) -> Option<&'static str> {
+        match plan {
+            LogicalPlan::Projection(_) => Some("derived_projection"),
+            LogicalPlan::Limit(_) => Some("derived_limit"),
+            LogicalPlan::Sort(_) => Some("derived_sort"),
+            LogicalPlan::Distinct(_) => Some("derived_distinct"),
+            LogicalPlan::Filter(filter) => {
+                Self::derived_input_alias(filter.input.as_ref())
+            }
+            LogicalPlan::Repartition(repartition) => {
+                Self::derived_input_alias(repartition.input.as_ref())
+            }
+            _ => None,
+        }
+    }
+
+    fn derived_input_scope<'a>(
+        plan: &'a LogicalPlan,
+        select: &SelectBuilder,
+    ) -> Option<DerivedInputScope<'a>> {
+        if select.inside_subquery_alias() {
+            return None;
+        }
+
+        match plan {
+            LogicalPlan::Projection(projection) => {
+                let alias = Self::derived_input_alias(projection.input.as_ref())?;

Review Comment:
   Whoa, I totally missed that case. Is there any part of the codebase you would recommend digging into so I can get better at catching cases like this in the future?



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