Undefined Index error with DB

[Sphinx111]

Having issues trying to combat the dreaded "Undefined index:" error with the "author_id" variable at line 6.

I can't quite see where I'm going wrong. The idea is to update some aspects of the database for my wife's book shop, but when I call the page, it loads with this variable problem. In the below example author_id is one of the fields of a table I created in an SQL database called author.

Maybe I just have my fundamentals wrong Either way, at least I can tell the missus I tried.

Code: Select all

<?php
 
include("dbinfo.inc.php");
$comm=@mysql_connect(localhost,$username,$password);
$rs=@mysql_select_db($database) or die( "Unable to select database"); 
$author_id = $_POST['author_id'];
echo "Reference: $author_id<br><BR>";
 
$sql="SELECT * FROM author WHERE reference='$author_id'";
$result=mysql_query($sql);
$num=mysql_num_rows($result);
$i=0;
while ($i < $num) {
$author_name=mysql_result($result,$i,"author_name"); ?>
 
++$i;
}
?>

P.S. I tried reading all the material I could on these forums, based on the Undefined index error, but no luck with regard to this situation.

[CloudedVision]

Line six is this line:

PHP: Select all

$author_id = $_POST['author_id']; 

And undefined index means one PHP can't find a certain section of an array, in this case $_POST['author_id']. So $_POST['author_id'] must not be set.

[Sphinx111]

Thank you for the swift response.

Excuse my illiteracy, but would I need to set the $_POST['author_id'] in a previous PHP page? Or amend the SQL database?

The table I am trying to access (a list of author's of books) has the primary key author_id; I thought it would be possible to identify the fields of this table via the key, and was using the aforementioned code to call that data, so that it could be edited if neccesary.

Regards.

[CloudedVision]

Undefined index 'author_id' means (In your situation) that there is no post data for author_id. So whatever form is submitting data to this query is not sending any information for author_id through POST. Either you've made an error and misnamed 'author_id' or the form data is being sent through GET or not at all.