当Mysql表中没有支付时，在php中从账单中减去支付

$servername = "数据库服务器地址";
$username = "数据库用户名";
$password = "数据库密码";
$dbname = "数据库名";

// 创建数据库连接
$conn = new mysqli($servername, $username, $password, $dbname);

// 检查连接是否成功
if ($conn->connect_error) {
    die("连接数据库失败: " . $conn->connect_error);
}

// 假设账单表名为bill，支付金额为payment
$billTable = "bill";
$payment = 100; // 假设支付金额为100

// 构建更新SQL语句
$sql = "UPDATE $billTable SET payment = payment - $payment WHERE payment > 0";

// 执行更新操作
if ($conn->query($sql) === TRUE) {
    echo "支付已从账单中减去成功";
} else {
    echo "更新账单失败: " . $conn->error;
}

// 关闭数据库连接
$conn->close();