PHP use mySQL to check existing username -

i have been following tutorial building simple registration / login script.

http://forum.codecall.net/topic/69771-creating-a-simple-yet-secured-loginregistration-with-php5/

i new php, have lot of experience using c++, thought transitions wouldn't hard, need figure out syntax. did very quick introduction mysql @ university, thought lot easier use mysql check existing username when user has registered, though knowledge isn't good. thought work;

select username codecalltut username = username; 

would work? selecting username database codecalltut , checks see if username being inputted username? if correct don't know how include in php.

i've tried using

$qry = "select username     codecalltut     username = username;" 

but syntax error when moves next statement.

<?php      $qry = "select username         codecalltut         username = username;"  //if register button clicked. } else { $usr = new users; //create new instance of class users $usr->storeformvalues( $_post ); //store form values  //if entered password match confirm password register him if( $_post['password'] == $_post['conpassword'] ) { echo $usr->register($_post);  } else { //if not must enter same password confirm box. echo "password , confirm password not match";  } }  ?> 

this query used construct database:

create database `codecalltut` default character set latin1 collate latin1_swedish_ci; use `codecalltut`;   create table if not exists `users` (   `userid` int(11) not null auto_increment,   `username` varchar(50) not null,   `password` varbinary(250) not null,   primary key (`userid`,`username`) ) engine=innodb  default charset=latin1 auto_increment=6 ; 

this html code when user clicks "register"

<li class="buttons">                          <input type="submit" name="register" value="register" />                             <input type="button" name="cancel" value="cancel" onclick="location.href='index.php'" />                      </li> 

your html form registration

<form action='' method='post'>     <input type='text' name='username' />     <input type='password' name='password' />     <input type='password' name='re-password' />     <input type='submit' name='submit' /> </form> 

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your php code

if($_post){          if(empty($_post['username']) && empty($_post['password']) && empty($_post['re-password'])) {             echo 'please enter fields';         }else {          $username = $_post['username'];         $password = $_post['password'];         $re_password = $_post['re-password'];          if($password !== $re_password){             echo 'both passwords not match';         }else {              $db_name =              $db_user =              $db_pass =               $conn = new pdo('mysql:host=localhost;dbname=xxx', 'xxx', 'xxx',                  array( pdo::attr_persistent => true )         );              $stmt = $conn->prepare("select username,password users username = ? , password = ?");             $stmt->execute(array($username, $password));              if($stmt->rowcount() === 0 ) {               $stmt = $conn->prepare("insert users (username, password) values (?,?)");             $stmt->execute(array($username, $password));             if($stmt->rowcount() ===1){                 echo 'registration complete';             }else {                 echo 'sorry, unknown error: please try again later';              }              }else {                 echo 'sorry, username '.$username.' exists';             }            }          }     }