PHP changing old mysql_query to PDO

Question

I have some old mysql_query queries in my code which i want to convert in to PDO but am struggling to get to work.

my original code was:

mysql_query("UPDATE people SET price='$price', contact='$contact', fname='$fname', lname='$lname' WHERE id='$id' AND username='$username' ")
or die(mysql_error()); 

now i am trying:

$sql = "UPDATE people SET price='$price', contact='$contact', fname='$fname', lname='$lname' WHERE id='$id' AND username='$username'";
$q   = $conn->query($sql) or die("failed!");

but can't seem to get it to work, any ideas?

UPDATED CODE:

$conn = new PDO("mysql:host=$host;dbname=$db",$user,$pass);


 // check if the form has been submitted. If it has, process the form and save it to the   database
 if (isset($_POST['submit']))
 { 
 // confirm that the 'id' value is a valid integer before getting the form data
 if (is_numeric($_POST['id']))
  {
 // get form data, making sure it is valid
 $id = $_POST['id'];
 $fname = mysql_real_escape_string(htmlspecialchars($_POST['fname']));
 $lname = mysql_real_escape_string(htmlspecialchars($_POST['lname']));
 $contact = mysql_real_escape_string(htmlspecialchars($_POST['contact']));
 $price = mysql_real_escape_string(htmlspecialchars($_POST['price']));


 // check that firstname/lastname fields are both filled in
 if ($fname == '' || $lname == '' || $contact == '' || $price == '' )
 {
 // generate error message
 $error = 'ERROR: Please fill in all required fields!';

 //error, display form
 renderForm($id, $fname, $lname, $contact, $price, $error);
 }
 else
 {
 // save the data to the database
 $username = $_SESSION['username'];

 $query = "UPDATE people 
         SET price=?, 
             contact=?, 
             fname=?, 
             lname=? 
          WHERE id=? AND 
                username=?";
$stmt = $db->prepare($query);
$stmt->bindParam(1, $price);
$stmt->bindParam(2, $contact);
$stmt->bindParam(3, $fname);
$stmt->bindParam(4, $lname);
$stmt->bindParam(5, $id);
$stmt->bindParam(6, $username);    
$stmt->execute();


 // once saved, redirect back to the view page
header("Location: view.php"); 
}

Answer 1

For more information visit this link: PHP PDO

based on your example,

<?php

    $query = "UPDATE people 
             SET price=?, 
                 contact=?, 
                 fname=?, 
                 lname=? 
              WHERE id=? AND 
                    username=?";
    $stmt = $dbh->prepare($query);
    $stmt->bindParam(1, $price);
    $stmt->bindParam(2, $contact);
    $stmt->bindParam(3, $fname);
    $stmt->bindParam(4, $lname);
    $stmt->bindParam(5, $id);
    $stmt->bindParam(6, $username);    
    $stmt->execute();

?>

PDO Prepared statements and stored procedures