diff --git a/mod/data/field/date/field.class.php b/mod/data/field/date/field.class.php
index bc35d4aea25..50236392dea 100755
--- a/mod/data/field/date/field.class.php
+++ b/mod/data/field/date/field.class.php
@@ -113,7 +113,18 @@ class data_field_date extends data_field_base {
     }
 
     function get_sort_sql($fieldname) {
-        return 'CAST('.$fieldname.' AS unsigned)';
+         global $CFG;
+ 
+         switch ($CFG->dbfamily) {
+             case 'postgres':
+             case 'mssql':
+                 return 'CAST('.$fieldname.' AS bigint)';
+             case 'oracle':
+                 return 'TO_NUMBER('.$fieldname.')';
+             case 'mysql':
+             default:
+                 return 'CAST('.$fieldname.' AS signed)';
+         }
     }