Nested while doesn't work in PHP - php

Question

I have problem with my code.
I use nested while in my code and the nested while doesn't work, only the outer while is work
I don't know where is the bug of my code.
This is the piece of my code :
$database = new mysqli('127.0.0.1', 'user', 'user', 'mini_email');
$query = 'SELECT * FROM mails';
$query2 = 'SELECT * FROM users';
$result_set = $database->query($query);
$result2 = $database->query($query2);
while ($row2 = $result2->fetch_assoc()) {
if ($row2['username'] == $_SESSION['user']) {
$id_email = $row2['id'];
}
}
if (isset($_SESSION['is_logged_in'])) {
echo('<center><font size="10">Mailing List</font></center><br><br>');
echo('<center><table border="3" bgcolor="#f0cdfa">');
echo('<tr>');
echo ('<td>No</td>');
echo ('<td>ID</td>');
echo ('<td>From</td>');
echo('<td>Subject</td>');
echo ('<td>Message</td>');
echo ('<td>Action</td>');
echo ('</tr>');
$i = 1;
while ($row = $result_set->fetch_assoc()) {
if ($row['to_user_id'] == $id_email) {
echo('<tr>');
echo ('<td>' . $i . '</td>');
echo ('<td>' . $row['id'] . '</td>');
while($row2 = $result2->fetch_assoc()){
if($row2['id']== $row['from_user_id']){
echo ('<td>' . $row2['username'] . '</td>');
}
}
echo ('<td>' . $row['subject'] . '</td>');
echo ('<td>' . $row['message'] . '</td>');
echo ('<td>View</td>');
echo ('</tr>');
$i++;
}
}

Answer 1

Your initial
while ($row2 = $result2->fetch_assoc()) {
is looping through all the records to the end of the set,
so looping a second time won't retrieve any further records because you're already at the end of the resultset
Resultset pointers aren't automatically reset when you initiate a new loop, but you can reset them manually using
$result2->data_seek(0);
before each subsequent loop
But iterating the point made in the comments by #Sirko you'd be better using a JOIN to make a single query

Answer 2

If I may help, I think you shouldn't even perform the queries when your if statement with the session returns false.
In the first lines or your script you should define a function with all this code, and write it like this :
function YourFunction()
{
if (isset($_SESSION['is_logged_in'])) {
return false;
}
// Database connection and queries
// your business
}
This will be more clean.
Next, your query doesn't seem to be correct. You get all the mails of your website, and then in a loop you check if the mail user id is the user id you have in session. Imagine the lack of performance if you have 35 000 mails in your database.
Improve your query with a WHERE statement : http://www.w3schools.com/sql/sql_where.asp
then, are you sure that $_SESSION['user'] contains an id ? I think your second if statement never returns true because of that.