php - Mysql XAMPP 不要将负值插入行中

Question

如何告诉数据库不接受、插入或更新来自 php 计算的负值。

考虑这个 php 代码:

<?php include('index2.php'); ?>
<?php include('db.php'); ?>
<?php
$mobile = $_SESSION['mobile'];
$date = date('M-d,Y H:i:s');
$date2 = date('M-d,Y');

if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
}
$amount = $_POST['amount'];
$balance = $_POST['balance'];

$balancenow = $balance - $amount; 

if ($amount > $balance) {
    $sql3 = "UPDATE users SET balance = '$balancenow'
    WHERE mobile = '$mobile'";        

    if ($conn->query($sql3) === TRUE) {
        echo  '<a href="index2.php"></a>';
    } else {
        echo "0";
    }
} else {
    echo '<script language="javascript">';
        echo 'alert("You don't have enough coupon balance")';
    echo '</script>';
    echo '<a href="index2.php"></a>';
} 
$conn->close();
?>

现在考虑上面的例子:“金额”为 500，余额为 250，这反过来给我们计算:

$balancenow = $balance - $amount;

= 250-500 = -250

现在在这种情况下，如何告诉数据库不接受负值并给出 else 语句..

感谢任何帮助..

Answer 1

好吧，我认为从数据库端验证是正确的选择，它迫使程序员以正确的方式编写代码。

将列架构更新为 UNSIGNED INT 以仅存储非负值

Unsigned type can be used to permit only nonnegative numbers in a column or when you need a larger upper numeric range for the column. For example, if an INT column is UNSIGNED, the size of the column's range is the same but its endpoints shift from -2147483648 and 2147483647 up to 0 and 4294967295.

您还可以验证来自 PHP 的数据，但它是第二级。