set session variable to user_id when user logs in - php

Question

I'm setting up a login/logout and I'm trying to send the users id number to other pages in the website so that I can manipulate the database when I want.
I use a query to match email/password and log in user(n.b. this is not the full code and not the problem, I'm matching emails and passwords)
$find= mysqli_query("SELECT * FROM users WHERE email='$ema' and password="$pw");
Then I fetch an array and start a session which I then check on pages further on in the website.
if(mysql_num_rows($find) == 1){
$row = mysql_fetch_array($result, MYSQL_BOTH);
$id= $row ['id'];
session_start();
$_SESSION['Login']= $id;
// Redirect - I use JS to send users to next page
}
else {
echo '<script type="text/javascript">';
echo 'alert("Invalid Username or Password");';
echo 'history.back();';
echo '</script>';
}
mysql_close($link);
On other pages I have code that checks for the session and redirects users if they aren't logged in. Here's that code:
<?php
session_start();
if(!isset($_SESSION['Register'])){
if(!isset($_SESSION['Login'])){
header("location:../notLoggedIn.php");
}
}
$get_id = $_SESSION['Register'];
$get_id = $_SESSION['Login'];
?>
Then, when I check what's in the id variable passed from the login page with this:
$profile = mysql_query("SELECT * FROM profiles WHERE id= $id");
var_export($id);
I get a null value. What's going wrong?

Answer 1

You must check if session is not started then use session_start();
if (session_status() == PHP_SESSION_NONE) {//php >5.4
session_start();
}
and use $_SESSION['Login'] instead of $id
$profile = mysql_query("SELECT * FROM profiles WHERE id=".$_SESSION['Login']);

Answer 2

Multiple mistakes i have seen.
1)First revise your query :
$find= mysqli_query("SELECT * FROM users WHERE email='$ema' and password='$pw');
2) Secondly start session on the top of file.
3) mysqli_close($link); instead of mysql_close($link);
4) In the Last check if the session is properly set.
if(isset($_SESSION['Login'])) {
$get_id = $_SESSION['Login'];
$profile = mysql_query("SELECT * FROM profiles WHERE id= $id");
var_export($id);
}

Answer 3

Hi Please note these points
1) Start session_start on the top of page (before any echo or white space).
2) I don't see your $_SESSION['Register']. Have you set it
3) You are passing session variable not simple variable so use this
$profile = mysql_query("SELECT * FROM profiles WHERE id = $_SESSION['Login']");
var_export( $_SESSION['Login']);
As $id will be null here always