fix

src/Interpreters/InterpreterInsertQuery.cpp

@@ -140,9 +140,11 @@ Block InterpreterInsertQuery::getSampleBlock(
 /** A query that just reads all data without any complex computations or filetering.
   * If we just pipe the result to INSERT, we don't have to use too many threads for read.
   */
-static bool isTrivialSelect(const ASTSelectQuery & select_query)
+static bool isTrivialSelect(const ASTPtr & select)
 {
-    const auto & tables = select_query.tables();
+    if (auto select_query = select->as<ASTSelectQuery>())
+    {
+        const auto & tables = select_query->tables();
 
         if (!tables)
             return false;
@@ -160,14 +162,17 @@ static bool isTrivialSelect(const ASTSelectQuery & select_query)
             return false;
 
         /// Note: how to write it in more generic way?
-    return (!select_query.distinct
+        return (!select_query->distinct
-        && !select_query.limit_with_ties
+            && !select_query->limit_with_ties
-        && !select_query.prewhere()
+            && !select_query->prewhere()
-        && !select_query.where()
+            && !select_query->where()
-        && !select_query.groupBy()
+            && !select_query->groupBy()
-        && !select_query.having()
+            && !select_query->having()
-        && !select_query.orderBy()
+            && !select_query->orderBy()
-        && !select_query.limitBy());
+            && !select_query->limitBy());
+    }
+    /// This query is ASTSelectWithUnionQuery subquery
+    return false;
 };
 
 
@@ -196,8 +201,9 @@ BlockIO InterpreterInsertQuery::execute()
         auto new_query = std::dynamic_pointer_cast<ASTInsertQuery>(query.clone());
         if (select.list_of_selects->children.size() == 1)
         {
-            auto & select_query = select.list_of_selects->children.at(0)->as<ASTSelectQuery &>();
+            if (auto select_query = select.list_of_selects->children.at(0)->as<ASTSelectQuery>())
-            JoinedTables joined_tables(Context(context), select_query);
+            {
+                JoinedTables joined_tables(Context(context), *select_query);
 
                 if (joined_tables.tablesCount() == 1)
                 {
@@ -207,7 +213,7 @@ BlockIO InterpreterInsertQuery::execute()
                         const auto select_with_union_query = std::make_shared<ASTSelectWithUnionQuery>();
                         select_with_union_query->list_of_selects = std::make_shared<ASTExpressionList>();
 
-                    auto new_select_query = std::dynamic_pointer_cast<ASTSelectQuery>(select_query.clone());
+                        auto new_select_query = std::dynamic_pointer_cast<ASTSelectQuery>(select_query->clone());
                         select_with_union_query->list_of_selects->children.push_back(new_select_query);
 
                         new_select_query->replaceDatabaseAndTable(storage_src->getRemoteDatabaseName(), storage_src->getRemoteTableName());
@@ -216,6 +222,7 @@ BlockIO InterpreterInsertQuery::execute()
                     }
                 }
             }
+        }
 
         auto storage_dst = std::dynamic_pointer_cast<StorageDistributed>(table);
 
@@ -277,10 +284,8 @@ BlockIO InterpreterInsertQuery::execute()
             {
                 const auto & selects = query.select->as<ASTSelectWithUnionQuery &>().list_of_selects->children;
 
-                is_trivial_insert_select = std::all_of(selects.begin(), selects.end(), [](const ASTPtr & select)
+                is_trivial_insert_select
-                {
+                    = std::all_of(selects.begin(), selects.end(), [](const ASTPtr & select) { return isTrivialSelect(select); });
-                    return isTrivialSelect(select->as<ASTSelectQuery &>());
-                });
             }
 
             if (is_trivial_insert_select)

src/Parsers/ASTSelectWithUnionQuery.cpp

@@ -48,6 +48,7 @@ void ASTSelectWithUnionQuery::formatQueryImpl(const FormatSettings & settings, F
         }
         else
         {
+            if (it != list_of_selects->children.begin())
                 settings.ostr << settings.nl_or_ws;
             (*it)->formatImpl(settings, state, frame);
         }

src/Storages/SelectQueryDescription.cpp

@@ -98,20 +98,35 @@ void checkAllowedQueries(const ASTSelectQuery & query)
 
 }
 
+/// check if only one single select query in SelectWithUnionQuery
+static bool isSingleSelect(const ASTPtr & select, ASTPtr & res)
+{
+    auto new_select = select->as<ASTSelectWithUnionQuery &>();
+    if (new_select.list_of_selects->children.size() != 1)
+        return false;
+    auto & new_inner_query = new_select.list_of_selects->children.at(0);
+    if (auto _ = new_inner_query->as<ASTSelectQuery>())
+    {
+        res = new_inner_query;
+        return true;
+    }
+    else
+        return isSingleSelect(new_inner_query, res);
+}
+
 SelectQueryDescription SelectQueryDescription::getSelectQueryFromASTForMatView(const ASTPtr & select, const Context & context)
 {
-    auto & new_select = select->as<ASTSelectWithUnionQuery &>();
+    ASTPtr new_inner_query;
 
-    if (new_select.list_of_selects->children.size() != 1)
+    if (!isSingleSelect(select, new_inner_query))
         throw Exception("UNION is not supported for MATERIALIZED VIEW", ErrorCodes::QUERY_IS_NOT_SUPPORTED_IN_MATERIALIZED_VIEW);
 
-    auto & new_inner_query = new_select.list_of_selects->children.at(0);
     auto & select_query = new_inner_query->as<ASTSelectQuery &>();
     checkAllowedQueries(select_query);
 
     SelectQueryDescription result;
     result.select_table_id = extractDependentTableFromSelectQuery(select_query, context);
-    result.select_query = new_select.clone();
+    result.select_query = select->as<ASTSelectWithUnionQuery &>().clone();
     result.inner_query = new_inner_query->clone();
 
     return result;