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

@@ -169,9 +169,15 @@ impl<'a, S: ContextProvider> SqlToRel<'a, S> {
         // factors, and those can never be the first factor in a FROM list. This
         // means we arrived here through the `for` loop in `plan_from_tables` or
         // the `for` loop in `plan_table_with_joins`.
-        let old_from_schema = planner_context.set_outer_from_schema(None).unwrap();
+        let old_from_schema = planner_context
+            .set_outer_from_schema(None)
+            .unwrap_or_else(|| Arc::new(DFSchema::empty()));
         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

@@ -3103,6 +3103,19 @@ fn join_on_complex_condition() {
     quick_test(sql, expected);
 }
 
+#[test]
+fn lateral_constant() {
+    let sql = "SELECT * FROM j1, LATERAL (SELECT 1) AS j2";
+    let expected = "Projection: j1.j1_id, j1.j1_string, j2.Int64(1)\
+            \n  CrossJoin:\
+            \n    TableScan: j1\
+            \n    SubqueryAlias: j2\
+            \n      Subquery:\
+            \n        Projection: Int64(1)\
+            \n          EmptyRelation";
+    quick_test(sql, expected);
+}
+
 #[test]
 fn lateral_comma_join() {
     let sql = "SELECT j1_string, j2_string FROM
@@ -3145,7 +3158,7 @@ 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\