php - 通过 PHP 从 MySQL 数据库中提取不同的单一值

Question

我有一个 SQL 语句，它从订单表中提取一个值(OrderID)。

"SELECT DISTINCT (MAX(OrderID)) FROM orders WHERE Username = 'hello@hello.com';

我通过 PHPMyAdmin 运行它，它为该用户返回一个订单 ID，这正是我想要的。但是，我正在尝试在 PHP 中运行它...

"SELECT DISTINCT (MAX(OrderID)) FROM orders WHERE Username = '". $_SESSION['Username'] ."'";

我希望提取订单 ID，以便我可以设置 $OrderID =(select 语句的结果)，然后运行如下更新语句。

$sql = "UPDATE orders SET Status = 'Failed' WHERE Status = 'Success' and OrderID = ". $OrderID ."";

如果我硬编码 $OrderID = 90; 它可以正常工作，但我需要通过登录者的 session 来获取 OrderID。

完整代码:

<?php
$url = 'http://' . $_SERVER['SERVER_NAME'] . $_SERVER['REQUEST_URI'];

if (strpos($url,'order-failed') !== false) {
    $servername = "NULL";
    $username = "NULL";
    $password = "NULL";
    $dbname = "NULL";

    // Create connection
    $conn = new mysqli($servername, $username, $password, $dbname);

    // Check Connection
    if ($conn->connect_error) {
        die("Connection failed: " . $conn->connect_error);
    }

    $query = "SELECT DISTINCT (MAX(OrderID)) FROM orders WHERE Username = '". $_SESSION['Username'] ."'";
    echo $query . "<br />";

    $OrderID = 93;
    echo $OrderID;
    echo "<br />";
    $sql = "UPDATE orders SET Status = 'Failed' WHERE Status = 'Success' and OrderID = ". $OrderID ."";
    echo $sql;

    if ($conn->query($sql) === TRUE) {
        echo "<br />Record updated successfully";
    }

    else {
        echo "<br />Error updating record: " . $conn->error;
    }

    $conn->close();
}

else {
    session_destroy();
}
?>

Answer 1

看起来这会有同样的效果......

$sql = "
UPDATE orders 
   SET Status = 'Failed' 
 WHERE Status = 'Success'
   AND Username = '{$_SESSION['Username']}'
 ORDER 
    BY OrderID DESC 
 LIMIT 1;
    ";

...虽然显然重写它以使用准备好的语句语法