php - Check if a username and email already exists in my database -

i new php , check whether or not username or email exists in database. if does, redirect signup page. code have works add users cannot figure out how check if username , email exist. don't want make either primary key please help!!! code have book using:

<?php require_once "app_config.php"; require_once "database_connection.php";  $upload_dir = host_www_root . "uploads/profile_pics/"; $image_fieldname = "user_pic";  //potential php errors $php_errors = array(1 => 'maximum file size in php.ini exceeded',                     2 => 'maximum file size in html form exceeded',                     3 => 'only part of file uploaded',                     4 => 'no file selected upload');  $first_name = trim($_request['first_name']); $last_name = trim($_request['last_name']); $username = trim($_request['username']); $password = trim($_request['password']); $email = trim($_request['email']); $bio = trim($_request['bio']); $facebook_url = str_replace("facebook.org", "facebook.com", trim($_request['facebook_url'])); $position = strpos($facebook_url, "facebook.com"); if($position === false) {     $facebook_url = "http://www.facebook.com/" . $facebook_url; } $twitter_handle = trim($_request['twitter_handle']); $twitter_url = "http://www.twitter.com/"; $position = strpos($twitter_handle, "@"); if($position === false) {     $twitter_url = $twitter_url . $twitter_handle; } else {     $twitter_url = $twitter_url . substr($twitter_handle, $position + 1); }  //make sure didn't have error uploading image ($_files[$image_fieldname]['error'] == 0)     or handle_error("the server couldn't upload image selected",                     $php_errors[$_files[$image_fieldname]['error']]);  // file result of valid upload? @is_uploaded_file($_files[$image_fieldname]['tmp_name'])     or handle_error("you trying naughty. shame on you!",                     "uploaded request: file named " .                     "'{$_files[$image_fieldname]['tmp_name']}'");  // image? @getimagesize($_files[$image_fieldname]['tmp_name'])     or handle_error("you selected file picture " .                     "that isn't image.",                     "{$_files[$image_fieldname]['tmp_name']} " .                     "isn't valid image file.");  //name file uniquely $now = time(); while(file_exists($upload_filename = $upload_dir . $now .                     '-' . $_files[$image_fieldname]['name'])) {     $now++; }  // insert image images table $image = $_files[$image_fieldname]; $image_filename = $image['name']; $image_info = getimagesize($image['tmp_name']); $image_mime_type = $image_info['mime']; $image_size = $image['size']; $image_data = file_get_contents($image['tmp_name']);  //insert images query $insert_image_sql = sprintf("insert images " .                         "(filename, mime_type, file_size, image_data) " .                     "values ('%s', '%s', %d, '%s');",                         mysql_real_escape_string($image_filename),                         mysql_real_escape_string($image_mime_type),                         mysql_real_escape_string($image_size),                         mysql_real_escape_string($image_data));  mysql_query($insert_image_sql)     or die(mysql_error());  //insert users query $insert_sql = sprintf("insert users " .                         "(first_name, last_name, username, " .                         "password, email, " .                         "bio, facebook_url, twitter_handle, " .                         "profile_pic_id) " .             "values ('%s', '%s', '%s', '%s', '%s',                     '%s', '%s', '%s', %d);",                         mysql_real_escape_string($first_name),                         mysql_real_escape_string($last_name),                         mysql_real_escape_string($username),                         mysql_real_escape_string($password),                         mysql_real_escape_string($email),                         mysql_real_escape_string($bio),                         mysql_real_escape_string($facebook_url),                         mysql_real_escape_string($twitter_handle),                         mysql_insert_id());  //insert user database mysql_query($insert_sql)     or die(mysql_error());  //redirect user page displays user information header("location: show_user.php?user_id=" . mysql_insert_id()); exit(); 

?>

select count(1) users email = '[insert username check here]' 

getting 0 means there no users username.

you'll want lower case usernames prior insertion prevent 'bob' vs. 'bob' vs. 'bob' scenario.