{
  local $db3->{RaiseError}=0;
  $sth_minus = $db3->prepare_cached("
       SELECT $column_list FROM $database_user_1.$table_names_r->[0]".'@'."$config{database_dblink_1}
       MINUS
       SELECT $column_list FROM $database_user_2.$table_names_r->[0]".'@'."$config{database_dblink_2}
  ");
  warn "prepare fails with $db3->errstr" if $db3->err;
}