Detect if username exsists

programming
1

Im trying to see if a username is already taken.


$query = mysql_query("SELECT * FROM members_tbl WHERE username = ' ".$_POST['username']." '");//Edit the query to fit your needs
                        $result = mysql_num_rows($query);
                        
                        if($result[0] === ($username)) {
                            echo "The username you have chosen is available"; //Does not exist!
                        }else{
                            echo "The username you have chosen already exists!"; //It is there
                        }

Whats wrong with my code?