multiple join query in cideigniter

public function winner(){
$current_time = date('Y-m-d h:i:s');
$select = array('BI.id', 'BI.product_id', 'BI.user_id', 'BI.amount');
$this->db->select($select);
$this->db->select_max('BI.amount');
$this->db->from('bidding as BI');
$this->db->join('product as PR', 'PR.id=BI.product_id', 'inner');
$this->db->where('PR.end_date <', $current_time);
$query = $this->db->get();

if($numrows = $query->num_rows()>0)
{
if($numrows == 1)
{
 $this->db->insert("bid_winner", $query->row());
 $pid = $this->db->insert_id();
 $sql = "SELECT `product_id` FROM `bid_winner` WHERE `id` = '".$pid."'";
 $query_delete = $this->db->query($sql);
 $product_del = $query_delete->result_array();
 $this->db->where('product_id', $product_del[0]['product_id']);
 $this->db->delete('bidding');
}elseif($numrows > 1){
 $this->db->insert_batch("bid_winner", $query->result_array());
}
return $pid;
}
else
{
return false;
}
}