要获取的上一行值 [英] Previous row value to be fetched

问题描述

在这里，我想将上一行的余额值输入到我的字段中。

Here I want to get the previous row balance value in to my field.

customer_id'16'的余额的最后一个ID是200，但我想将先前的id值获取到字段中，这就是我的表

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

这是我的模型

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();
}

这是我的控制权

 public function final_payment($order_code)
{
    $data['active_mn']='';
    $data['result'] = $this->Account_model->order_balance($order_code); 
    $this->load->view('final_payment',$data);
}

我的服务表如下：

    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     

我的结果应该是这样的：

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

推荐答案

这里的一个选择是使用<$ c自连接$ c> payment 表，并连接到 customer_id 和 order_id 列。您可以添加另一个join函数调用，然后在选择的结果中使用它。以下解决方案使用原始查询，因为Codeigniter在连接条件下似乎不容许算术运算：

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();
}

查询的格式为：

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

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