diff --git a/dblayeroo.php b/dblayeroo.php
index 4b670ec..1c65b34 100644
--- a/dblayeroo.php
+++ b/dblayeroo.php
@@ -1577,6 +1577,12 @@ class dblayeroo
           // expression, if not already done
           if ($this->groupByExpression === null)
           {
+            // Set to empty array to demonstrate that a GROUP BY is needed, but
+            // there is no already defined displayed Columns.
+            // Used if the group by is called from join object
+            if ($this->displayColumn === null)
+              $this->groupByExpression = array ();
+            else
               $this->groupByExpression = $this->displayColumn;
           }
           if ($func === "GROUP_CONCAT" && ($pos = strpos ($name, ",'")))
@@ -2099,11 +2105,35 @@ class dblayeroo
   public function groupByGet ($full=false)
   /* {{{ */
   {
-    $groupBy = array ();
+    $groupBy = null;
     if ($this->joinObject)
       $full = true;
+    if ($this->joinObject)
+    {
+      foreach ($this->joinObject as $obj)
+      {
+        $ext = $obj->groupByGet (true);
+        if ($ext !== null)
+        {
+          if (! is_array ($groupBy))
+            $groupBy = array ();
+          $groupBy = array_merge ($groupBy, $ext);
+        }
+      }
+
+    }
+    // If there is some GROUP BY in join Object, but not in this object, all
+    // the displayed fields must be added to be added in the GROUP BY
+    if (is_array ($groupBy) &&
+         (is_null ($this->groupByExpression) ||
+         (is_array ($this->groupByExpression) &&
+           empty ($this->groupByExpression))
+       ))
+      $this->groupByExpression = $this->displayColumn;
     if (is_array ($this->groupByExpression))
     {
+      if (! is_array ($groupBy))
+        $groupBy = array ();
       foreach ($this->groupByExpression as $pos=>$o)
       {
         if ($full !== false)
@@ -2113,16 +2143,8 @@ class dblayeroo
           $groupBy[$pos] = $o;
       }
     }
-    if ($this->joinObject)
-    {
-      foreach ($this->joinObject as $obj)
-      {
-        $ext = $obj->groupByGet (true);
-        if ($ext !== null)
-          $groupBy = array_merge ($groupBy, $obj->groupByGet (true));
-      }
-    }
-    ksort ($groupBy, SORT_NATURAL);
+    if (is_array ($groupBy))
+      ksort ($groupBy, SORT_NATURAL);
     return $groupBy;
   }
   /* }}} */