Php 仅当字段中的值等于或大于输入值时，如何从MySQL表中的值减去用户输入值？

我有一个表单，其中包含输入字段

项目id

，

员工id

，以及

数量

。每当有新闻发布时，我想更新一个表。我想要我提交的值，即只有当它小于或等于目标表中已经存在的数量值时才要减去的数量。 下面是我的代码

表格：

<?php
$con = mysql_connect("localhost","root","");
if (!$con)
{
    die('Could not connect: ' . mysql_error());
}

mysql_select_db("dbtest", $con);

$result = mysql_query ("SELECT * FROM recieved_orders");
echo "<table border = '1' style='margin-left:18px;margin-right:18px;' bgcolor='#CFC'>
                <tr>
                    <th bgcolor='#34495E' colspan='9'>
                        <h1><font color='white' align='center'>&nbsp&nbsp&nbspORDER OFFICE SUPPLIES</font></h1>
                    </th>
                </tr>
                <tr bgcolor='#CFC' font size='18'>
                    <th>Item Id</th>
                    <th>Staff Id</th>
                    <th>Quantity</th>
                </tr>";

        while ($row = mysql_fetch_array($result))
        {
            echo "<form action=\"Updateisue.php\" method=\"post\" enctype=\"multipart/form-data\">";
                echo "<tr>";
                    echo "<td><input type=\"text\" name=\"ItemId\"  size=\"30\" value=\" ". $row ['ItemId'] . "\" readonly></td>";
                    echo "<td><input type=\"text\" name=\"StaffId\" value=\" ". $row ['StaffId'] . "\" readonly></td>";
                    echo "<td><input type=\"text\" name=\"Quantity\" value=\" ".$row ['Quantity'] . "\" readonly></td>";
                    echo "<td><input type=\"submit\" name=\"submit\" size=\"30\" style='background-color:#3366FF' value=\"ISSUE  \"></td>";
                echo "</tr>";
            echo "</form>";
        }
echo "</table>";
mysql_close($con);
?>

<?php
include './database-config.php';
$searchError = "";
$searchMessage = "";

function sanitizeString($var) {
    $var = htmlentities($var);
    $var = strip_tags($var);
    $var = stripslashes($var);
    $var = trim($var);
    return $var;
}
$ItemId = sanitizeString($_POST['ItemId']);
$Quantity = sanitizeString($_POST['Quantity']);

if($Quantity<=Quantity){
    $updatePassQuery = "UPDATE stationery SET Quantity=Quantity-$Quantity WHERE ItemId='$ItemId'";
    $executeQuery = mysqli_query($dbh,$updatePassQuery);
if($executeQuery){
    echo " update successful";
    $message  = "update was successful";
    header("location: procurementhome.php");

    } else{
        echo "unsuccessful";
        $error = "update failed";
        // header("location: upstationery.php");
    }
}
else
{
    echo "no more itmes";
}
?>

1）
不允许在
内。检查

2）您必须保留一个提交按钮以查看所有详细信息。在那里做任何更改并提交

3）根据第2点，输入的
名称必须是数组类型。（检查下面的答案）

4）在Updateisue.php中，使用
for loop
或
foreach
查找每个
ItemId
并执行查询

5）在这行
如果（$quantity这是什么
$QuantityHi@musyimi：你没有回答。你能提供一些关于你的代码的详细信息吗？例如，到底是什么不起作用或者你在哪里遗漏了解决方案？
<?php
$con = mysql_connect("localhost","root","");
if (!$con)
{
    die('Could not connect: ' . mysql_error());
}

mysql_select_db("dbtest", $con);
$result = mysql_query ("SELECT * FROM recieved_orders");

echo "<form action=\"Updateisue.php\" method=\"post\" enctype=\"multipart/form-data\">";
    echo "<table border = '1' style='margin-left:18px;margin-right:18px;' bgcolor='#CFC'>
                    <tr>
                        <th bgcolor='#34495E' colspan='9'>
                            <h1><font color='white' align='center'>&nbsp&nbsp&nbspORDER OFFICE SUPPLIES</font></h1>
                        </th>
                    </tr>
                    <tr bgcolor='#CFC' font size='18'>
                        <th>Item Id</th>
                        <th>Staff Id</th>
                        <th>Quantity</th>
                    </tr>";

            while ($row = mysql_fetch_array($result))
            {
                    echo "<tr>";
                        echo "<td><input type=\"text\" name=\"ItemId[]\"  size=\"30\" value=\" ". $row ['ItemId'] . "\" readonly></td>";
                        echo "<td><input type=\"text\" name=\"StaffId[]\" value=\" ". $row ['StaffId'] . "\" readonly></td>";
                        echo "<td><input type=\"text\" name=\"Quantity[]\" value=\" ".$row ['Quantity'] . "\" readonly></td>";
                        echo "<td><input type=\"submit\" name=\"submit\" size=\"30\" style='background-color:#3366FF' value=\"ISSUE  \"></td>";
                    echo "</tr>";
            }
            echo "<tr><td colspan='3'></td><td><input type=\"submit\" name=\"submit\" size=\"30\" style='background-color:#3366FF' value=\"ISSUE  \"></td></tr>";
    echo "</table>";
echo "</form>";

mysql_close($con);

?>

<?php
include './database-config.php';
$searchError = "";
$searchMessage = "";

function sanitizeString($var) {
    $var = htmlentities($var);
    $var = strip_tags($var);
    $var = stripslashes($var);
    $var = trim($var);
    return $var;
}

$totalItem = sizeof($_POST['ItemId']);
$Quantity = $_POST['Quantity'];
for($i=0;$i<$totalItem;$i++) {

    $CItemId = sanitizeString($ItemId[$i]);
    $CQuantity = sanitizeString($Quantity[$i]);

    $quantityAvailable = mysqli_query("SELECT Quantity FROM stationery WHERE ItemId='$CItemId ");
    $row = mysqli_fetch_array($quantityAvailable,MYSQLI_ASSOC); 
    $quantityDB = $row['Quantity'];

    if($CQuantity<=$quantityDB){
        $updatePassQuery = "UPDATE stationery SET Quantity=Quantity-$CQuantity WHERE ItemId='$CItemId'";
        $executeQuery = mysqli_query($dbh,$updatePassQuery);
        if($executeQuery){
            echo " update successful";
            $message  = "update was successful";
            header("location: procurementhome.php");
        } else{
                echo "unsuccessful";
                $error = "update failed";
        }
    }
    else
    {
        echo "no more itmes";
    }
}

?>