diff --git a/core/modules/views/src/Plugin/views/query/Sql.php b/core/modules/views/src/Plugin/views/query/Sql.php
index 421c8b1..3aed415 100644
--- a/core/modules/views/src/Plugin/views/query/Sql.php
+++ b/core/modules/views/src/Plugin/views/query/Sql.php
@@ -1233,6 +1233,7 @@ public function query($get_count = FALSE) {
       $this->hasAggregate = TRUE;
     }
     elseif ($this->hasAggregate == FALSE) {
+      // Allow 'GROUP BY' even no aggregation function has been set.
       $this->hasAggregate = $this->view->display_handler->getOption('group_by');
     }
     $groupby = array();