diff --git a/dblayeroo.php b/dblayeroo.php
index 13a87e6..965254d 100644
--- a/dblayeroo.php
+++ b/dblayeroo.php
@@ -1268,7 +1268,7 @@ class dblayeroo
   private $whereValues = array ();
   /** The columns in GROUP BY condition
     */
-  private $groupByExpression = array ();
+  private $groupByExpression = null;
   /** The ORDER expression
     */
   private $orderExpression = array ();
@@ -1930,6 +1930,8 @@ class dblayeroo
     $groupBy = array ();
     if ($this->joinObject)
       $full = true;
+    if ($this->groupByExpression === null)
+      return null;
     foreach ($this->groupByExpression as $pos=>$o)
     {
       if ($full !== false)
@@ -1941,7 +1943,11 @@ class dblayeroo
     if ($this->joinObject)
     {
       foreach ($this->joinObject as $obj)
-        $groupBy = array_merge ($groupBy, $obj->groupByGet (true));
+      {
+        $ext = $obj->groupByGet (true);
+        if ($ext !== null)
+          $groupBy = array_merge ($groupBy, $obj->groupByGet (true));
+      }
     }
     ksort ($groupBy, SORT_NATURAL);
     return $groupBy;
@@ -2064,7 +2070,7 @@ class dblayeroo
         $sql .= "\n WHERE ". implode (" ", $whereGetExpression);
       $groupByExpression = $this->groupByGet ();
       if (! empty ($groupByExpression))
-        $sql .= "\n GROUP BY ". implode (" ", $groupByExpression);
+        $sql .= "\n GROUP BY ". implode (",", $groupByExpression);
       if (count ($order))
         $sql .= "\n ORDER BY ". implode (",", $order);
       if (! empty ($this->limitExpression))