Question

我正在从事图书馆管理系统工作。并在更新字段中。如果用户没有传递数据，我希望保持我的数据不变，而不是将其更改为空白

<?php
if( isset($_POST['update']) )
{
    $conn = mysql_connect('localhost', 'root', '');
    if( !$conn )
    {
        die('Could not connect: ' . mysql_error());
    }
    $db_selected = mysql_select_db('library', $conn);
    $Book_ID     = $_POST['Book_ID'];
    $Book_Name   = $_POST['Book_Name'];
    $Author      = $_POST['Author'];
    $Quantity    = $_POST['Quantity'];

    $sql    = "update books set Book_Name='$Book_Name', Author='$Author', 
            Quantity='$Quantity' where Book_ID='$Book_ID'";
    mysql_select_db('test_db');
    $retval = mysql_query($sql, $conn);

    if( !$retval )
    {
        die('Could not update data: ' . mysql_error());
    }
    echo "Updated data successfully\n";
    header("refresh:2; url=updatebook.php");
    mysql_close($conn);
}
else
{
    ?>
    <form method = "post" action = "<?php $_PHP_SELF ?>">
        <table width = "400" border =" 0" cellspacing = "1" cellpadding = "2">
            <tr>
                <td width = "100">Book ID</td>
                <td><input name = "Book_ID" type = "number" id = "Book_ID"></td>
            </tr>
            <tr>
                <td width = "100">Book Name</td>
                <td><input name = "Book_Name" type = "text" id = "Book_Name"></td>
            </tr>
            <tr>
                <td width = "100">Author</td>
                <td><input name = "Author" type = "text" id = "Author"></td>
            </tr>
            <tr>
                <td width = "100">Quantity</td>
                <td><input name = "Quantity" type = "text" id = "Quantity"></td>
            </tr>

            <tr>
                <td width = "100"> </td>
                <td> </td>
            </tr>

            <tr>
                <td width = "100"> </td>
                <td>
            <tr>
                <td width = "100"> </td>
                <td> </td>
            </tr>

            <tr>
                <td width = "100"> </td>
                <td>
                    <input name = "update" type = "submit" id = "update" value = "Update">
                </td>
            </tr>
        </table>
    </form>
    <?php
}
?>

如果用户不想更改某个字段的值并将其保留为空白。我不想用空白更新该字段。我希望保留该字段的数据。

如果我输入图书编号并保留图书名称，则从此代码中删除，然后此代码传递值

Answer 1

您可以借助mysql中的简单if...else条件来完成此操作。

$sql = "UPDATE books SET
        Book_Name=IF(LENGTH('$Book_Name')=0, Book_Name, '$Book_Name'),
        Author=IF(LENGTH('$Author')=0, Author, '$Author'),
        Quantity=IF(LENGTH('$Quantity')=0, Quantity, '$Quantity')
        WHERE Book_ID='$Book_ID'";

不要对数据库使用直接查询。它就像是对Sql Injection的公开邀请。

Answer 2

如果变量为空，则需要首先获取原始值，然后使用IF ELSE来使用旧值而不是新值。请参阅我修改过的以下代码：

`

    $conn = mysql_connect('localhost', 'root', '');

    if(!$conn ) {
       die('Could not connect: ' . mysql_error());
    }
    $db_selected = mysql_select_db('library', $conn);
    $old_data = mysql_fetch_array(mysql_query("select * from books where Book_ID='".$_POST['Book_ID']."'"));

    $Book_ID = $_POST['Book_ID'];
    $Book_Name = ($_POST['Book_Name'] == '' ? $old_data['Book_Name'] : $_POST['Book_Name']);
    $Author = ($_POST['Author'] == '' ? $old_data['Author'] : $_POST['Author']);
    $Quantity = ($_POST['Quantity'] == '' ? $old_data['Quantity'] : $_POST['Quantity']);

    $sql = "update books set  Book_Name='$Book_Name', Author='$Author', 
    Quantity='$Quantity' where Book_ID='$Book_ID'";
    mysql_select_db('test_db');
    $retval = mysql_query( $sql, $conn );

    if(! $retval ) {
       die('Could not update data: ' . mysql_error());
    }
    echo "Updated data successfully\n";
    header("refresh:2; url=updatebook.php");

    mysql_close($conn);
 }else {
    ?>
       <form method = "post" action = "<?php $_PHP_SELF ?>">
          <table width = "400" border =" 0" cellspacing = "1" 
             cellpadding = "2">

             <tr>
                <td width = "100">Book ID</td>
                <td><input name = "Book_ID" type = "number" 
                   id = "Book_ID"></td>
             </tr>

             <tr>
                <td width = "100">Book Name</td>
                <td><input name = "Book_Name" type = "text" 
                   id = "Book_Name"></td>
             </tr>
             <tr>
                <td width = "100">Author</td>
                <td><input name = "Author" type = "text" 
                   id = "Author"></td>
             </tr>

             <tr>
                <td width = "100">Quantity</td>
                <td><input name = "Quantity" type = "text" 
                   id = "Quantity"></td>
             </tr>

             <tr>
                <td width = "100"> </td>
                <td> </td>
             </tr>

             <tr>
                <td width = "100"> </td>
                <td>
                <tr>
                <td width = "100"> </td>
                <td> </td>
             </tr>

             <tr>
                <td width = "100"> </td>
                <td>
                   <input name = "update" type = "submit" 
                      id = "update" value = "Update">
                </td>
             </tr>

          </table>
       </form>

    <?php
 }

＆GT？; `

使用php更新数据库时我遇到了一些问题

2 个答案: