Fix: fallback to local plan w/o PR in case of empty table

src/Interpreters/ClusterProxy/executeQuery.cpp

@@ -528,7 +528,7 @@ void executeQueryWithParallelReplicas(
     /// do not build local plan for distributed queries for now (address it later)
     if (settings.allow_experimental_analyzer && settings.parallel_replicas_local_plan && !shard_num)
     {
-        auto local_plan = createLocalPlanForParallelReplicas(
+        auto [local_plan, with_parallel_replicas] = createLocalPlanForParallelReplicas(
             query_ast,
             header,
             new_context,
@@ -536,6 +536,12 @@ void executeQueryWithParallelReplicas(
             coordinator,
             std::move(analyzed_read_from_merge_tree));
 
+        if (!with_parallel_replicas)
+        {
+            query_plan = std::move(*local_plan);
+            return;
+        }
+
         auto read_from_remote = std::make_unique<ReadFromParallelRemoteReplicasStep>(
             query_ast,
             new_cluster,

src/Processors/QueryPlan/ParallelReplicasLocalPlan.cpp

@@ -21,9 +21,7 @@
 namespace DB
 {
 
-void addConvertingActions(QueryPlan & plan, const Block & header, bool has_missing_objects);
-
-std::unique_ptr<QueryPlan> createLocalPlanForParallelReplicas(
+std::pair<std::unique_ptr<QueryPlan>, bool> createLocalPlanForParallelReplicas(
     const ASTPtr & query_ast,
     const Block & header,
     ContextPtr context,
@@ -68,7 +66,9 @@ std::unique_ptr<QueryPlan> createLocalPlanForParallelReplicas(
             node = nullptr;
     }
 
-    chassert(reading);
+    if (!reading)
+        /// it can happened if merge tree table is empty, - it'll be replaced with ReadFromPreparedSource
+        return {std::move(query_plan), false};
 
     ReadFromMergeTree::AnalysisResultPtr analyzed_result_ptr;
     if (analyzed_read_from_merge_tree.get())
@@ -89,7 +89,8 @@ std::unique_ptr<QueryPlan> createLocalPlanForParallelReplicas(
     node->step = std::move(read_from_merge_tree_parallel_replicas);
 
     addConvertingActions(*query_plan, header, /*has_missing_objects=*/false);
-    return query_plan;
+
+    return {std::move(query_plan), true};
 }
 
 }

src/Processors/QueryPlan/ParallelReplicasLocalPlan.h

@@ -8,7 +8,7 @@
 namespace DB
 {
 
-std::unique_ptr<QueryPlan> createLocalPlanForParallelReplicas(
+std::pair<std::unique_ptr<QueryPlan>, bool> createLocalPlanForParallelReplicas(
     const ASTPtr & query_ast,
     const Block & header,
     ContextPtr context,