Planner: use DFSchema::merge in create_relation_subquery

In order to compute the `set_outer_from_schema` argument we currently
use `DFSchema::join`. When we combine the current outer FROM schema with
the current outer query schema columns from the latter should override
columns from the first, so the correct way is to use `DFSchema::merge`.

To witness the fix, note that the query in the fixed test case isn't
planned as expected without the accompanying changes.

datafusion/sql/src/relation/mod.rs

@@ -161,7 +161,11 @@ impl<'a, S: ContextProvider> SqlToRel<'a, S> {
         // the `for` loop in `plan_table_with_joins`.
         let old_from_schema = planner_context.set_outer_from_schema(None).unwrap();
         let new_query_schema = match planner_context.outer_query_schema() {
-            Some(lhs) => Some(Arc::new(lhs.join(&old_from_schema)?)),
+            Some(old_query_schema) => {
+                let mut new_query_schema = old_from_schema.as_ref().clone();
+                new_query_schema.merge(&old_query_schema);
+                Some(Arc::new(new_query_schema))
+            }
             None => Some(Arc::clone(&old_from_schema)),
         };
         let old_query_schema = planner_context.set_outer_query_schema(new_query_schema);

datafusion/sql/tests/sql_integration.rs

@@ -3219,7 +3219,7 @@ fn lateral_comma_join_with_shadowing() {
     let sql = "\
             SELECT * FROM j1, LATERAL (\
               SELECT * FROM j1, LATERAL (\
-                SELECT * FROM j2 WHERE j1.j1_id = j2_id\
+                SELECT * FROM j2 WHERE j1_id = j2_id\
               ) as j2\
             ) as j2;";
     let expected = "Projection: j1.j1_id, j1.j1_string, j2.j1_id, j2.j1_string, j2.j2_id, j2.j2_string\