mySQL WHERE clause issue in PHP - php

Question

I have created a page where it lets users to edit their information which is stored in the database. However i can't get the WHERE clause to work it just keeps coming up with entry not found. Any help would be great thanks.!
<?php
mysql_connect('localhost', 'root', 'password') or die(mysql_error());
mysql_select_db("peopletank") or die(mysql_error());
$query = mysql_query("SELECT * FROM users WHERE id='$id'")
or die(mysql_error());
if(mysql_num_rows($query)>=1){
while($row = mysql_fetch_array($query)) {
$id = $row['id'];
$firstname= $row['firstname'];
$secondname= $row['secondname'];
}
?>
<form action="update.php" method="post">
<input type="hidden" name="ID" value="<?php echo $id;?>">
Value1: <input type="text" name="value1" value="<?php echo $firstname;?>">
<br>
Value2: <input type="text" name="value2" value="<?php echo $secondname?>">
<input type="Submit" value="Change">
</form>
<?php
}else{
echo 'No entry found. Go back';
}
?>

Answer 1

Try this :
$query = mysql_query("SELECT * FROM users WHERE id='".$id."'");
Make sure your $id is populated correctly. Try checking the value first if the query still didn't showed up like this :
echo 'The id is : '.$id;
$query = mysql_query("SELECT * FROM users WHERE id='".$id."'");
If the $id is populated correctly but still return no result then run the query manually in your mysql database, probably there is no result for specified $id
And while populating data, no need to fetch $id while you just have same $id ini this query.
while($row = mysql_fetch_array($query)) {
$id = $row['id']; /* << Remove this */
$firstname= $row['firstname'];
$secondname= $row['secondname'];
}

Answer 2

I aint 100% sure if its one of these things:
1) Try ending the statements with ;
2) Numbers dont have to be between ''
3) Try putting names of columns between ``
4) use LIMIT 1 where you can (makes things faster but not important)
5) Always try to use a selecter (faster)
<?
if ( $query = mysql_query("SELECT `firstname`,`secondname` FROM `users` WHERE (`id` = $id) LIMIT 1;"))
{
if ($r = mysql_fetch_assoc($query))
{
$firstname = $r['firstname'];
$secondname = $r['secondname'];
}
}
?>