php - 使用 php 表单或 mysql 查询对行执行计算

Question

我的英语有点弱希望你能理解，因为我最后试图给出例子。请帮助我，我是这个领域的新手。谢谢你。

我有一个表格如下

<form method="post">
<p>Amount:
<input type="text" name="receive" />
Registration:
<input type="text" name="reg_number" />
<input type="submit" name="submit_amount" value="Submit" /></p>
</form>

当我提交此表单时，将运行以下查询

if(isset($_POST['submit_amount']) && count($_POST)!==0){

                $receive=$_POST['receive'];
                $reg_number=$_POST['reg_number'];

                $sql="INSERT INTO `installments`(month, amount, receive, fk_users_id)
SELECT now(), installment, $receive, id
  FROM users
 WHERE reg_number = '$reg_number'";
                $result=mysqli_query($con,$sql);
                if($result){
                    echo "<script>
                    alert('amount inserted');
                    </script>";
                    }else{
                        die(mysqli_error($con));
                        }
                }

当此查询运行时，它会在用户表的 amount 列和表单的接收列中插入值

喜欢:

installment_id |   month    | prv_arrear | amount | total | receive | arrear | fk_user_id
        1        2014-09-13                 2500               2500                1

我想根据这个公式在prv_arrear、total和arrear列中插入值

公式:

prv_arrear + amount = total

total - reveive = arrear

查看示例

installment_id |    month    | prv_arrear | amount | total | receive | arrear | fk_user_id
1                 2014-09-12       0         2500     2500     1600     900        1
1                 2014-09-13      900        2500     3400     1600     900        1

注意:当所有值都插入列中时，拖欠列的值应位于 prv_arrear 中，如上例所示。

Answer 1

这个 mysql 语句应该可以做到。或者非常接近。

INSERT INTO `installments`(month, amount, prv_arrear, total, arrear, receive, fk_users_id)
SELECT now(), installment, installments.arrear, installment+installments.arrear, installment+installments.arrear-$receive, $receive, id
  FROM users LEFT JOIN installments ON users.id=installments.fk_users_id 
 WHERE reg_number = '$reg_number'
 ORDER BY month DESC LIMIT 1"