Session en php

<?php
session_start();
include "config/connexion.php";

//--------------------------------------
// Le temps des tests :
//echo "<pre> Variables POST :<br>";
//print_r($_POST);
//echo "</pre>";
//--------------------------------------

//********************************//
// Recupération des variables :
//********************************//
$user=isset($_POST['user']) && $_POST['user'] !=''?$_POST['user']:NULL;
$pass=isset($_POST['pass']) && $_POST['pass'] !=''?$_POST['pass']:NULL;

//********************************//
// Préparation de la requete:
//********************************//
$sql = "SELECT * FROM table_utilisateur
      WHERE user = '".$user."'
      AND pass = '".$pass."'";
     
//--------------------------------------
// Le temps des tests :
//echo "<pre> La Requete est :<br>";
//echo $sql;
//echo "</pre>";
//--------------------------------------

//********************************//
// Execution de la requete:
//********************************//     
$req= $connexion->prepare($sql);
$resultat = $req->execute();

 //--------------------------------------
 // Le temps des tests :
//echo "<pre>Resultat :<br>";
//print_r($resultat);
//echo "</pre>"; 
  //--------------------------------------

$NbRow = $req->fetch(PDO::FETCH_NUM);
 //--------------------------------------
 // Le temps des tests :
//echo "<pre> NbRows =".$NbRow[0] ."</pre>";
 //--------------------------------------
if ($NbRow >=1){
if ($_SESSION['user']=admin;) {
	unset($_SESSION['error_login']);
	header('Location: index2.php');}
	else
 $_SESSION['user']=$user;
 unset($_SESSION['error_login']);
  //--------------------------------------
 // Le temps des tests :
 //echo "<pre> Variables de session:<br>";
 //print_r($_SESSION);
 //echo "</pre>";
 //--------------------------------------
 header('Location: index.php');
 exit;
}else{
 // destruction des variables de session
 session_destroy();
 $_SESSION['error_login'] = "Login ou mot de passe incorrect!!!";
 //--------------------------------------
 // Le temps des tests :
 echo "<pre> Variables de session:<br>";
 //print_r($_SESSION);
 echo "</pre>";
 //--------------------------------------
 header('Location: login.php');
}
?>