canMaterializeQuery

server/src/main/java/org/apache/druid/server/ClientQuerySegmentWalker.java

@@ -432,7 +432,7 @@ private <T> DataSource inlineIfNecessary(
               dryRun
           );
         }
-      } else if (canRunQueryUsingLocalWalker(subQuery) || canRunQueryUsingClusterWalker(subQuery)) {
+      } else if (canMaterializeQuery(subQuery)) {
         // Subquery needs to be inlined. Assign it a subquery id and run it.
 
         final Sequence<?> queryResults;
@@ -516,6 +516,26 @@ private <T> DataSource inlineIfNecessary(
     }
   }
 
+  private boolean canMaterializeQuery(final Query query)
+  {
+      final DataSource dataSourceFromQuery = query.getDataSource();
+      final DataSourceAnalysis analysis = dataSourceFromQuery.getAnalysis();
+      final QueryToolChest<T, Query<T>> toolChest = warehouse.getToolChest(query);
+
+      // 1) Must be based on a concrete datasource that is not a table.
+      // 2) Must be based on globally available data (so we have a copy here on the Broker).
+      // 3) If there is an outer query, it must be handleable by the query toolchest (the local walker does not handle
+      //    subqueries on its own).
+      // 1) Must be based on a concrete table (the only shape the Druid cluster can handle).
+      // 2) If there is an outer query, it must be handleable by the query toolchest (the cluster walker does not handle
+      //    subqueries on its own).
+      boolean toolchestCanPerform = !(dataSourceFromQuery instanceof QueryDataSource)
+          || toolChest.canPerformSubquery(((QueryDataSource) dataSourceFromQuery).getQuery());
+      return toolchestCanPerform && analysis.isConcreteBased()
+          && (dataSourceFromQuery.isGlobal() || analysis.isTableBased());
+
+    }
+
   /**
    * Decorate query runners created by {@link #clusterClient}, adding result caching, result merging, metric
    * emission, etc. Not to be used on runners from {@link #localClient}, since we expect it to do this kind

sql/src/test/java/org/apache/druid/sql/calcite/CalciteJoinQueryTest.java

@@ -4369,7 +4369,6 @@ public void testUnionAllTwoQueriesLeftQueryIsJoin(Map<String, Object> queryConte
     );
   }
 
-  @NotYetSupported(Modes.UNION_WITH_COMPLEX_OPERAND)
   @MethodSource("provideQueryContexts")
   @ParameterizedTest(name = "{0}")
   public void testUnionAllTwoQueriesRightQueryIsJoin(Map<String, Object> queryContext)