Codeigniter Joining Tables - Passing Parameters - sql

Question

I'm attempting to join two tables while using codeigniter. I've done this same SQL query writing regular SQL. When I attempt to do the same in codeigniter, I keep getting errors. I'm not quite sure what I'm doing wrong. What do you guys think I'm doing wrong?
My function in model_data.php
function getJoinInformation($year,$make,$model)
{
//$this->db->distinct();
// here is where I need to conduct averages but lets just work on extracting info.
// from the database and join tables.
$this->db->select('*');
$this->db->from('tbl_car_description');
$this->db->join('tbl_car_description', 'd.id = p.cardescription_id');
$this->db->where('d.year', $year);
$this->db->where('d.make', $make);
$this->db->where('d.model', $model);
$result = $this->db->get();
/*
$query = $this->db->get_where('tbl_car_description',
array(
'year' => $year,
'make' => $make,
'model' => $model
)
);
if($query->num_rows()) return $query->result();
return null;
*/
}
My error message
A Database Error Occurred
Error Number: 1066
Not unique table/alias: 'tbl_car_description'
SELECT * FROM (`tbl_car_description`) JOIN `tbl_car_description` ON `d`.`id` = `p`.`cardescription_id` WHERE `d`.`year` = '2006' AND `d`.`make` = 'Subaru' AND `d`.`model` = 'Baja'
Filename: C:\wamp\www\_states\system\database\DB_driver.php
Line Number: 330
Here is the code written in SQL and it's working great. I want to do the something in codeigniter but I'm confused as to how. Any help would be much appreciated. Thanks everyone.
$sql_2 = mysql_query("SELECT ROUND(AVG(p.value),1) AS AvgPrice, ROUND(AVG(p.mileage),1) AS AvgMileage
FROM tbl_car_description d, tbl_car_prices p
WHERE (d.id = p.cardescription_id)
AND (d.year = '".$year."')
AND (d.make = '".$make."')
AND (d.model = '".$model."')
AND (p.approve = '1')");

Answer 1

Your CI query references the same table twice, which I assume is a typo. However, you only need include your table alias with the table name in your Active Record call:
//$this->db->distinct();
$this->db->select('*');
$this->db->from('tbl_car_description d');
$this->db->join('tbl_car_prices p', 'd.id = p.cardescription_id');
$this->db->where('d.year', $year);
$this->db->where('d.make', $make);
$this->db->where('d.model', $model);
$result = $this->db->get();

Answer 2

Couple issues: You need to include your table aliases and your join should have the name of the second table ...
$this->db->from('tbl_car_description AS d');
$this->db->join('tbl_car_prices AS p', 'd.id = p.cardescription_id');