php - Using isset with mysql_real_escape_string -

i'm new php , trying build log in system. aware it's insecure, college project in understanding basics of php, that's not problem.

i have usernames , passwords in table , trying store cookie if user types in correct username , password combination. want have pages can accessed if user logged in.

i keep getting undefined index notice. aware article http://notesofgenius.com/how-fix-php-notice-undefined-index/ need add isset somewhere, can't work out put in code. using isset mysql_real_escape_string confusing me.

i've connected database , started session in config.php. here code:

<?php  require("config.php"); $username = mysql_real_escape_string($_post['username']); $password = mysql_real_escape_string($_post['password']);    $result = mysqli_query($con,"select * users username='$username' , password='$password' "     ); if($row = mysqli_fetch_array($result)) { $_session['user'] = 'person'; header('location: postarticle.php'); } else{ echo "<p>incorrect password</p>"; } ?> 

thanks. apologies if has been asked before, did check couldn't find anything.

actually isset() has nothing escaping. there no connection between these 2 facilities.

also, isset() won't make code working if doesn't. can save error message in case calling page regular way, without sending form it. if keep getting message form sent - check form method , input name attributes.

anyway, don't need isset() here

<?php  if ($_server['request_method'] == 'post') {     require("config.php");     $username = mysqli_real_escape_string($con, $_post['username']);     $password = mysqli_real_escape_string($con, $_post['password']);        $sql = "select * users username='$username' , password='$password'";     $result = mysqli_query($con,$sql);     if($row = mysqli_fetch_array($result))     {         $_session['user'] = 'person';         header('location: postarticle.php');         exit;      } else {          echo "<p>incorrect password</p>";         exit;     } }