试图编辑/删除记录的sql数据库与php

我有一个表，我需要使用php编辑/删除sql数据库的行。问题(与时间一样古老的故事)是删除/编辑功能都不能正确工作。我没有得到任何错误消息，所以我花了几个小时梳理代码，在谷歌上搜索和搜索其他类似的问题，但没有任何问题真正解决我的具体问题。

我可能少了一个引号或类似的东西，但如果能给点提示就太好了。

这是我的编辑代码:

//if the 'id' variable is set in the URL, we know that we need to edit a record 
if (isset($_GET['GroomingID']))
{
    //if the form's submit button is clicked, we need to process the form
    if (isset($_POST['submit']))
    {
            //make sure the 'id' in the URL is valid
            if (is_numeric($_POST['GroomingID']))
                {
                    //get variables from the URL/form
                    $GroomingID = $_POST['GroomingID'];
                    $firstName = htmlentities($_POST['FirstName'], ENT_QUOTES);
                    $lastName = htmlentities($_POST['LastName'], ENT_QUOTES);
                //check that firstname and lastname are both not empty
                    if ($firstName == '' || $lastName == '')
                        {
                    //if they are empty, show an error message and display the form
                            $error = 'ERROR: Please fill in all required fields';
                            renderForm($firstName, $lastName, $error, $GroomingID);
                    }
                    else
                    {
                            //if everything is fine, update the record
                if($stmt = $link->prepare("UPDATE grooming SET FirstName = ?, LastName = ? WHERE GroomingID=?"))
            {
                    $stmt->bind_param("ssi", $firstName, $lastName, $GroomingID);
                    $stmt->execute();
                    $stmt->close();
            }
            //show an error message if the query encounters an error
            else
            {
                echo "Error: could not preapre sql statement.";
            }
            //redirect the user once the form is updated
            header("Location: PS_Manage_Appnts.php");
            exit();
        }
    }
    //if the 'id' variable isn't valid, show error message
    else
    {
        echo "Error";
    }
}
    //if the form hasn't been submitted yet, get the info from the database and show the form
    else
    {
        //make sure the 'id' value is valid
        if (is_numeric($_GET['GroomingID']) && $_GET['GroomingID'] > 0)
        {
            //get 'id' from URL
            $id = $_GET['GroomingID'];
            //get the record from the database
            if($stmt = $link->prepare("SELECT * FROM grooming WHERE GroomingID=?"))
                {
                    $stmt->bind_param("i", $GroomingID);
                    $stmt->execute();
                    $stmt->bind_result($GroomingID, $firstName, $lastName);
                    $stmt->fetch();
                //show the form
                renderForm($firstName, $lastName, NULL, $GroomingID);
                $stmt->close();
            }
            //show an error if the query has an error
            else
            {
                echo "Error: could not prepare SQL statement.";
            }
        }
//if the 'id' value is not valid, redirect the user back to the PS_Manage_Appnts.php page
        else {
                header("location:PS_Manage_Appnts.php");
                exit();
             }
        }
}

我的删除代码(与编辑代码分开):

<?php
//connect to the database
include ("newDBconn.php");
//confirm that the 'id'(in this case, 'GroomingID') variable has been set 
    if (isset($_GET['GroomingID']) && is_numeric($_GET['GroomingID']))
    {
    //get the 'id' variable from the URL
    $GroomingID = $_GET['GroomingID'];
    //delete record from the database
    if ($stmt = $link->prepare("DELETE FROM grooming WHERE GroomingID = '?' LIMIT 1"))
        {
            $stmt->bind_param("i", $GroomingID);
            $stmt->execute();
            $stmt->close();
        }
        else
        {
            echo "ERROR: could not prepare sql statement.";
        }
        $link->close();
        // redirect user after delete is successful
        header ("location:PS_Manage_Appnts.php");
        exit();
    }
    else
    //if the 'id' variable isn't set, redirect the user
    {
        header("location:PS_Manage_Appnts.php");
        exit();
    }
?>

最后，我的数据库连接的代码在一个单独的php文件:

<?php
//connect to db
$link = mysqli_connect('localhost', 'root', 'pwdpwd', 'pet_shop');
//check connection
if (!$link) {
    printf("Connection failed: %s'n", mysqli_connect_error());
    exit();
}
?>

注意:我知道msql注入，但是a)这是在我的机器上的测试，b)我想先解决这个问题。谢谢你的帮助!

编辑:我通过FireFox的Firebug运行了这个，也没有出现错误。但是，我注意到，当单击表上的'delete'链接时，firebug显示如下:

https://i.stack.imgur.com/8HlIk.png

没有代码链接上面带下划线的css文件到我的删除文件(PS_delete_post.php)，所以我不知道为什么它试图抓取css文件。PS_delete_post.php开头不应该有任何css链接。

EDIT2:根据Neo的建议，我已经将$firstName/$lastName变量更改为所有小写。现在，当单击"edit"时，用户将(正确地)被引导到一个空表单中输入值，但是点击submit 将添加一个新行，而不是编辑一个现有行。