如何避免在 php while 循環中的 SQL db 中多次扣除庫存？

Question

當我有很多人在我的網站上下訂單后嘗試結帳時，我遇到了問題。 我使用while循環來確保訂購的數量從我的SQL數據庫中的可用數量中扣除，但不是按計划扣除，而是扣除多余的。

我做錯了嗎？

<?php
//Database connection
include("db/config.php");

//Session to get user id
$user_id=$_SESSION['id'];
$statuss='added';

   $value2='';

    //Query to fetch last inserted invoice number and create a new invoice number 
    $query = "SELECT invoice_no from invoice order by invoice_no DESC LIMIT 1";
    $stmt = $conn->query($query);
    if(mysqli_num_rows($stmt) > 0) {
        if ($row = mysqli_fetch_assoc($stmt)) {
            $value2 = $row['invoice_no'];
            $value2 = substr($value2, 10, 13);//separating numeric part
            $value2 = $value2 + 1;//Incrementing numeric part
            $value2 = "ARW/19-20/" . sprintf('%03s', $value2);//concatenating incremented value
            $value = $value2; 
        }
    } 
    else {
        $value2 = "ARW/19-20/001";
        $value = $value2;
    }
    // echo $value;
if(isset($_POST['check_out'])){

   //Main code

//Get all input values
$name=mysqli_real_escape_string($conn,$_POST['name']);
    $phone=mysqli_real_escape_string($conn,$_POST['phone']);
    $address=mysqli_real_escape_string($conn,$_POST['address']);
    $payment_method=mysqli_real_escape_string($conn,$_POST['payment_mtd']);

$added='added';
//Get session name     $user_name=$_SESSION['name'];

//Query to update order operation table
        $sql="UPDATE order_operation SET name='$name', user_name='$user_name', phone='$phone', address='$address',payment='$payment_method' WHERE user_id=$user_id AND status='$added'";   
        if($conn->query($sql) === TRUE){
//Declare variables       
$before='added';
$status='completed';

//Update order operation with created invoice number

$sql="UPDATE order_operation SET status=?, invoice_no=? WHERE user_id='$user_id' AND status='$before'";
            $stmt=$conn->prepare($sql); 
            $stmt->bind_param('ss',$status,$value);
            if($stmt->execute()){
                $sql="INSERT INTO invoice(invoice_no,user_id) VALUES('$value','$user_id')";
                $conn->query($sql);
                    //Deduct from stock
                    $sql = "SELECT * FROM `order_operation` WHERE invoice_no='$value'";
                    $sql_run = mysqli_query($conn, $sql);

                    while ($row = mysqli_fetch_array($sql_run)) {
 //Deduct from stock since the order id's meet the requirements                                         $deduct=$row['stock_quantity'] - $row['quantity'];
                            $stock_id=$row['stock_id'];
                           $connector= "UPDATE stocks SET quantity =  '$deduct' WHERE id = $stock_id" ;
                           if($conn->query($connector) === TRUE){

$_SESSION['customer_name']=$name;   
                                $_SESSION['phone']=$phone;
                                $_SESSION['address']=$address;
                                $_SESSION['payment']=$payment_method;
                                $_SESSION['invoice_no']=$row['invoice_no'];
                                header('location:order_invoice.php');

                           }else{
                            echo $conn->error;
                           }

}
                        //End of deduct from stock

                    $conn->close();

                 }else{
                    die($conn->error);

                 }
             }else{

                 die($conn->error);

             }

$stmt->close();
               $conn->close();

}

?>

Answer 1

SELECT后跟取決於它的UPDATE始終是競爭條件。 使用來自以下的多表更新：

UPDATE order_operation oo, stocks s
SET s.quantity = s.quantity - MIN(oo.stock_quantity, s.quantity),
    oo.stock_quantity = MIN(oo.stock_quantity, s.quantity)
WHERE s.id = oo.stock_id
  AND oo.invoice_id = X

數量的附加條件可確保庫存水平和訂單不超過可用庫存，但您可能希望以另一種方式執行此操作以確保訂單對減少感到滿意。

如果您發現自己在循環中執行 SQL ，那么數據庫語法很有可能會做得更好。

還要查找准備好的語句並在mysqli_real_escape_string變體上使用這些語句。