Fixed: group by bugs

src/Driver/Base.php

@@ -557,7 +557,7 @@ class Base
     {
         $this->groupBy = null;
         if (!empty($fields)) {
-            $fileds = is_array($fields) ? join(', ', $fields) : $fields;
+            $fields = is_array($fields) ? join(', ', $fields) : $fields;
             $this->groupBy = sprintf($this->_query['GROUP'], $fields);
         }
         return $this;