diff --git a/dblayeroo.php b/dblayeroo.php
index 2985d24..0b2dbf4 100644
--- a/dblayeroo.php
+++ b/dblayeroo.php
@@ -1533,16 +1533,29 @@ class dblayeroo
       {
         $func = strtoupper (trim (substr ($name, 0, $pos)));
         $name = trim (substr ($name, $pos+1, -1));
+        $separator = "";
         if (in_array ($func, array ("AVG", "COUNT", "GROUP_CONCAT", "MAX",
                                     "MIN","SUM")))
         {
+          $aggregateFunction = true;
           // Aggregate function. Add the non aggregate fields to the GROUP BY
           // expression, if not already done
           if ($this->groupByExpression === array ())
           {
-            $aggregateFunction = true;
             $this->groupByExpression = $this->displayColumn;
           }
+          if ($func === "GROUP_CONCAT" && ($pos = strpos ($name, ",'")))
+          {
+            // There is a comma: the developper add the separator string
+            $separator = addslashes (substr ($name, $pos + 2, -1));
+            $name = substr ($name, 0, $pos);
+            if ($this->driver === "sqlite" || $this->driver === "psql")
+              $separator = ",'$separator'";
+            elseif ($this->driver === "mysql")
+              $separator = " SEPARATOR '$separator'";
+          }
+          if ($func === "GROUP_CONCAT" && $this->driver === "psql")
+            $func = "string_agg";
         }
         $display = "$func($name)";
       }
@@ -1554,12 +1567,13 @@ class dblayeroo
         $this->displayColumn[$getSortOrder] = $this->sep.$display.$this->sep;
       else
         $this->displayColumn[$getSortOrder] =
-          "$func($this->sep$name$this->sep)";
+          "$func($this->sep$name$this->sep$separator)";
       if ($this->groupByExpression !== array () && ! isset ($aggregateFunction))
       {
         // Not a aggregate function, but groupBy is set : add the new field name
         $this->groupByExpression[$getSortOrder] = $this->sep.$name.$this->sep;
       }
+      unset ($aggregateFunction);
     }
     return $this;
   }
@@ -1585,7 +1599,7 @@ class dblayeroo
     }
     if ($name[0] !== $this->sep)
       $name = $this->sep.$name;
-    if (substr ($name, -1) !== $this->sep)
+    if (! isset ($func) && substr ($name, -1) !== $this->sep)
       $name = $name.$this->sep;
     if ($full !== false)
       $name = $this->sep.$this->tableprefix.$this->table.$this->sep.".".$name;