How to debug why a DELETE query is not working, in PHP?

Question

Here is the error I am receiving:

Notice: Undefined index: id in C:\EasyPHP-12.1\www\final project\book\admin\process_del_contact.php on line 9 can't Execute...

And here is my code:

$link=mysql_connect("localhost","root","")or die("Can't Connect...");

        mysql_select_db("shop",$link) or die("Can't Connect to Database...");



        $query="delete from contact where con_id =".$_GET['id'];

        mysql_query($query,$link) or die("can't Execute...");


        header("location:contact.php");

MySQL database:

con_id / con_nm / con_email /con_query

score 3 · Answer 1 · answered May 07 '14 at 14:10

Some advises for the future:

Never ever use GET parameters when you do writes in the database (yes DELETE is also a write)
Always check the input before you pass it to the database sever (in_array, isset, array_key_exists)
Always validate your input and cast them to the proper type manually before you use them.
Always use prepared statements and parameter binding when you use parameters in your query.
Do not use mysql_* functions, they are deprecated, use mysqli_* or PDO instead

The problem with your query is how you build it. You did not checked that the 'id' key exists or not in your $_GET array.

Also, please try to figure out what will happen if I send this as the 'id' GET parameter: 1 OR 1=1

+1 suggestion Do not use the root user in production environment to acces the database! Create a new user and grant the required (and only the required) permissions.

score 1 · Answer 2 · answered May 07 '14 at 14:10

1

Try adding single quotes within the query:

$query="delete from contact where con_id ='" . $_GET['id'] . "'";

answered May 07 '14 at 14:10

dckuehn

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score 0 · Answer 3 · answered May 07 '14 at 14:30

make it simplier, try to make new variable for 'id' :

$id = $_GET["id"];
$query = mysql_query ("delete from contact where con_id = '$id'");
if($query) {
    echo "deleting data success";
} else {
    echo "deleting data failed".mysql_error();
}

and make sure your code is connected with the database. sorry bad english

How to debug why a DELETE query is not working, in PHP?

3 Answers3