ASK: how to get table name of the current query

[eluser]Unknown[/eluser]
thanks for the solution..
i've try use the custom function call..
there are some error reports says:
"An Error Was Encountered This feature is not available for the database you are using"
do i write the wrong code or something?
here are my codes:

<?
$query= $this->db->query('select * from sub where id=2');
$row = $query->row();
echo $this->db->call_function('mysql_field_table','$query','$row->id');
?>

thanks..