  Item_trigger_field(THD *thd, Name_resolution_context *context_arg,
                     row_version_type row_ver_arg,
                     const LEX_CSTRING *field_name_arg,
                     ulong priv, const bool ro)
    :Item_field(thd, context_arg,
               (const char *)NULL, (const char *)NULL, field_name_arg),
     row_version(row_ver_arg), field_idx((uint)-1), original_privilege(priv),
     want_privilege(priv), table_grants(NULL), read_only (ro)
  {}