PHP MySQL选择总和不工作

我做了一些研究，研究了如何在MySQL中合计一列的值，发现

SELECT SUM

是最好的方法，但我花了几个小时试图解决这个问题，但仍然无法实现：

代码如下：

// Create connection
$conn = new mysqli($servername, $username, $password, $dbname);
// Check connection
if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
} 

$result = mysqli_query('SELECT SUM(price) AS value_sum FROM xCarts_'. $useXsesh .'_sandwiches'); 
$row = mysqli_fetch_assoc($result); 
$sum = $row['value_sum'];

echo $sum;
mysqli_close($conn);

这是桌子：

---

您正在使用OOP样式连接到数据库，然后尝试使用过程样式获取数据

您需要将过程转换为OOP

这句话：

$result = mysqli_query('SELECT SUM(price) AS value_sum FROM xCarts_'. $useXsesh .'_sandwiches'); 
$row = mysqli_fetch_assoc($result); 
$sum = $row['value_sum'];

应如下所示：

$result = $conn->query('SELECT SUM(price) AS value_sum FROM xCarts_'. $useXsesh .'_sandwiches'); 
$row = $result->fetch_assoc(); 
$sum = $row['value_sum'];

$result = mysqli_query($conn, 'SELECT SUM(price) AS value_sum FROM xCarts_'. $useXsesh .'_sandwiches');
//                     ^^^^^
$row = mysqli_fetch_assoc($result); 

$sum = $row['value_sum'];

---

如果需要保留程序样式，请使用程序样式连接到mysqli：

$conn = mysqli_connect($servername, $username, $password, $dbname);

if (!$conn) {
    die("Connection failed: " . mysqli_connect_error());
} 

然后将连接传递到mysqli_*函数，如下所示：

$result = $conn->query('SELECT SUM(price) AS value_sum FROM xCarts_'. $useXsesh .'_sandwiches'); 
$row = $result->fetch_assoc(); 
$sum = $row['value_sum'];

$result = mysqli_query($conn, 'SELECT SUM(price) AS value_sum FROM xCarts_'. $useXsesh .'_sandwiches');
//                     ^^^^^
$row = mysqli_fetch_assoc($result); 

$sum = $row['value_sum'];

---

您正在使用OOP样式连接到数据库，然后尝试使用过程样式获取数据

您需要将过程转换为OOP

这句话：

$result = mysqli_query('SELECT SUM(price) AS value_sum FROM xCarts_'. $useXsesh .'_sandwiches'); 
$row = mysqli_fetch_assoc($result); 
$sum = $row['value_sum'];

应如下所示：

$result = $conn->query('SELECT SUM(price) AS value_sum FROM xCarts_'. $useXsesh .'_sandwiches'); 
$row = $result->fetch_assoc(); 
$sum = $row['value_sum'];

$result = mysqli_query($conn, 'SELECT SUM(price) AS value_sum FROM xCarts_'. $useXsesh .'_sandwiches');
//                     ^^^^^
$row = mysqli_fetch_assoc($result); 

$sum = $row['value_sum'];

---

如果需要保留程序样式，请使用程序样式连接到mysqli：

$conn = mysqli_connect($servername, $username, $password, $dbname);

if (!$conn) {
    die("Connection failed: " . mysqli_connect_error());
} 

然后将连接传递到mysqli_*函数，如下所示：

$result = $conn->query('SELECT SUM(price) AS value_sum FROM xCarts_'. $useXsesh .'_sandwiches'); 
$row = $result->fetch_assoc(); 
$sum = $row['value_sum'];

$result = mysqli_query($conn, 'SELECT SUM(price) AS value_sum FROM xCarts_'. $useXsesh .'_sandwiches');
//                     ^^^^^
$row = mysqli_fetch_assoc($result); 

$sum = $row['value_sum'];

---

你的问题很好。也许您的“id”属性不是数字类型

您的查询很好。也许您的“id”属性不是数字类型

价格列是否为int（或非文本/字符串的内容）？是，设置为int（20）侧注：SQL注入…价格列是否为int（或非文本/字符串的内容）？是，设置为int（20）侧注：SQL注入。。。