PHP function to perform SQL query not working - php

Question

I am trying to use a function to perform an SQL query and return the result. Doing a manual SQL query with the same query as the below works and returns the correct result but doing it within PHP is not working at all (page is blank).
connection.php
<?php
require_once("settings.php");
$conn = oci_connect($db_user, $db_pass, $db_ip.'/'.$db);
if (!$conn) {
$e = oci_error();
trigger_error(htmlentities($e['message'], ENT_QUOTES), E_USER_ERROR);
}
?>
functions.php
<?php
require_once("connection.php");
function GetInvoice($n)
// returns invoice number for given order number
{
$stid = oci_parse($conn, 'SELECT InvoiceNo FROM Orders WHERE OrderNo = $n');
oci_define_by_name($stid, 'InvoiceNo', $InvoiceNo);
oci_execute($stid);
echo "$InvoiceNo";
}
GetInvoice(999645);
?>
Doing the manual SQL query shows a resulting InvoiceNo, it is just not working in PHP.
Thanks
Steve

Answer 1

You are trying to use a variable outside of function inside the function. That variable is not in function's scope. Due to this, $conn is undefined. Also, you have used $InvoiceNo withoud fetch result, I did some refoctoring on that place. You can use following;
function GetInvoice($n, $conn)
// returns invoice number for given order number
{
$stid = oci_parse($conn, 'SELECT InvoiceNo FROM Orders WHERE OrderNo = $n');
oci_define_by_name($stid, 'InvoiceNo', $InvoiceNo);
oci_execute($stid);
while (oci_fetch($stid)) {
echo "$InvoiceNo";
}
}
GetInvoice(999645, $conn);

Answer 2

The parameters you are passing in functions, seems undefined
as you have created your function needs only one parameter, then from where this will get this variable $InvoiceNo
oci_define_by_name($stid, 'InvoiceNo', $InvoiceNo);