Setting a variable via the sessions once logged in - php

Question

Logging in we of course have set the $_SESSION['username'] and $_SESSION['password'] as usual. However I am then trying to pack that into a variable for use around the site:
$logged = mysql_query("SELECT * FROM `users` WHERE `username`='$_SESSION['username']' AND password = '$_SESSION['password']'");
$logged = mysql_fetch_array($logged);
One previous setups, this has enabled me to then use $logged around the site for various reasons, such as calling the logged in users email to echo in a form,
However, this time, when using this method, it fails to echo anything. I have tried using the session username variable which works to echo the username, but then I tried using the session to echo the email and it didn't work.
If someone could help me pinpoint why this is, I'd be grateful.
It just doesn't seem to be pulling any information from the user as it should.

Answer 1

For me this just seems like an escape-thing. Try
$logged = mysql_query("SELECT * FROM users WHERE username='".$_SESSION['username']."' AND password = '".$_SESSION['password']."'");
$logged = mysql_fetch_array($logged);
Also make sure to call session_start(); before sending any headers/echoing anything if you weren't aware.
Off topic-tip
As long as this query isn't used in anything public, it's fine. But if you're gonna use this code for anything, be sure to slash your query variables. If not, and if my credentials are not validated nor hashed, you could do some nasty SQL injection by setting your password to be something like '; DELETE * FROM USERS;# as the query would then say SELECT * FROM users WHERE username='JohnDoe' AND password = ''; DELETE * FROM USERS;#'

Answer 2

for the usage of session
if(!session_id())
session_start();
the above session start is a must in every page.
use print_r($_SESSION); to check the session variables initialized..
once done (try using mysqli insted of mysql)
$sql='SELECT col1, col2, col3 FROM table1 WHERE condition';
$rs=$conn->query($sql);
if($rs === false) {
trigger_error('Wrong SQL: ' . $sql . ' Error: ' . $conn->error, E_USER_ERROR);
} else {
$arr = $rs->fetch_all(MYSQLI_ASSOC);
}
foreach($arr as $row) {
echo $row['co1'];
}
comment your progress for further changes..