Previous row value to be fetched - mysql

Question

Here I want to get the previous row balance value in to my field.
The last id of customer_id '16' of balance is 200, but I want to get the previous ids value in to the field and this is my table
id order_id customer_id amount actual_amount paid_amount balance type
25 11 16 100.00 50.00 50.00 Cash
26 12 16 200.00 100.00 100.00 Cash
27 13 16 150.00 100.00 50.00 Cash
28 14 16 300.00 250.00 50.00 Cash
29 14 16 170.00 100.00 70.00 Cash
30 15 16 100 170.00 70.00 100.00 Cash
31 16 16 400 500.00 300.00 200.00 Cash
this is my model
public function order_balance($order_code)
{
$this->db->join('services','payment.customer_id=services.customer_id','left');
$this->db->select('payment.*,payment.balance,payment.actual_amount,payment.customer_id');
$this->db->order_by('payment.id','desc');
$query = $this->db->get_where('payment',array('code' => $order_code));
return $query->previous_row();
}
This is my control:
public function final_payment($order_code)
{
$data['active_mn']='';
$data['result'] = $this->Account_model->order_balance($order_code);
$this->load->view('final_payment',$data);
}
My services table looks like this:
id code customer_id particulars
11 ORD00011 16 phone
12 ORD00012 16 gdf
13 ORD00013 16 ghgfh
14 ORD00014 16 tv
15 ORD00015 16 ghfg
16 ORD00016 16 tv
17 ORD00017 16 gdfg
18 ORD00018 16 desk
19 ORD00019 16 gdf
My result should be like this:
id order_id customer_id amount actual_amount paid_amount balance type
31 16 16 400 500.00 300.00 100.00 Cash

Answer 1

One option here would be to do a self join with the payment table, joining on the customer_id and order_id columns. You can add another join function call and then use the result in your select. The following solution uses a raw query since Codeigniter does not seem to tolerate arithmetic in the join condition:
public function order_balance($order_code)
{
$this->db->query("SELECT p1.*, p2.balance AS previous_balance FROM payment p1 INNER JOIN payment p2 ON p1.order_id = p2.order_id + 1 AND p1.customer_id = p2.customer_id LEFT JOIN services s ON p1.customer_id = s.customer_id ORDER BY p1.id DESC");
$query = $this->db->get_where('p1', array('code' => $order_code));
return $query->previous_row();
}
The query has the form:
SELECT p1.*, p2.balance AS previous_balance
FROM payment p1 INNER JOIN payment p2
ON p1.order_id = p2.order_id + 1 AND
p1.customer_id = p2.customer_id
LEFT JOIN services s
ON p1.customer_id = s.customer_id
ORDER BY p1.id DESC

Answer 2

There are lots of ways of writng this. Here's one way. I don't know codeigniter, so you'll have to reverse engineer it...
SELECT a.id
, a.order_id
, a.customer_id
, a.amount
, a.actual_amount
, a.paid_amount
, b.balance
, a.type
FROM
( SELECT x.*
, MAX(y.id) prev
FROM payment x
JOIN payment y
ON y.id < x.id
AND y.customer_id = x.customer_id
GROUP
BY x.id
) a
JOIN payment b
ON b.id = a.prev
ORDER
BY id DESC LIMIT 1;