Simple Login Page And Its Code For Creating Sassion

Here you can create user sassion and detect Login Errors by this form. Easy and simple code for newbies.

 <?php session_start(); ?>  
 <?php require_once("includes/connection.php"); ?>  
 <?php  
      if(!isset($_SESSION['username']))  
      {  
           $error= array();  
           if(isset($_POST['submit']))  
           {  
                //Get values from form  
                $username = $_POST['username'];  
                $password = $_POST['password'];  
                $query = "select * from users where username = '" . mysql_real_escape_string($username) . "'";  
                $query_run = mysqli_query($connection, $query);  
                if(!$query_run)  
                     echo 'username, password query is not working well. <br />' . mysqli_connect_error();  
                if(mysqli_num_rows($query_run) != 0 )  
                {  
                     $user = mysqli_fetch_array($query_run);  
                     if($username == $user['username'])  
                     {                      
                          if($password == $user['password'])  
                          {  
                               $_SESSION['username'] = $username;  //User session is created here
                               header("Location: index.php");  
                               exit;  
                          }  
                          else  
                          {  
                               array_push($error, 'password Wrong');  
                          }  
                     }  
                     else  
                     {  
                          array_push($error, 'Username Wrong');  
                     }  
                }  
                else  
                {  
                     array_push($error, 'Login Error');  
                }  
           }  
      }  
      else  
      {  
           header('Location: signup.php');  
           exit;  
      }  
 ?>  
 <div align="left" style="float:right">  
 <h2 align="center">Login Panel for Developer</h2>  
 <form method="post" action="login.php">  
      <label for="username">Username: </label><input name="username" type="text" id="username" /><br />  
   <label for="password">Password: </label><input type="password" name="password" id="password" /><br />  
   <input type="submit" name="submit" value="Login" />  
 </form>  
 <?php  
      if(isset($_POST['submit']))  
                {  
                     echo $error[0];  
                }  
           ?>  
 </div>