how to do this..[query inside query]

[eluser]Bluemagix[/eluser]
how can i do this type of thing in codeigniter

Code:

$sql="SELECT * FROM category WHERE parentid=0";
$result=mysql_query($sql);
while($row=mysql_fetch_assoc($result))
{
echo $row["name"]."<br />";
$sub_sql="SELECT * FROM category WHERE parentid='".$row["id"]."'";
$sub_result=mysql_query($sub_sql);
while($sub_row=mysql_fetch_assoc($sub_result))
{
  echo "- ".$sub_row["name"]."<br />";
  }
}