The best practise when to use PHP exception handling
<?php public function index() {

    $this->database->query("SELECT user_name, FROM test WHERE user_name = :user_name");

    $this->database->execute_query("jim");

    $this->view->data = $this->database->fetch_query();

  ?>

<?php

class DB {

    private $datasourcename;
    private $user;
    private $password;
    private $connection;
    private $prepare;
    private $query;

    function __construct($dsn, $user, $password) {

        $this->datasourcename = $dsn;
        $this->user = $user;
        $this->password = $password;


        $this->connection = new PDO($this->datasourcename, $this->user, $this->password);
    }

    public function query($query) {

        $this->query = $query;
        try {
            if (empty($query)) {

                throw new Exception("The query is empty");
                return false;
            }
        } catch (Exception $e) {
            echo 'Caught exception: ', $e->getMessage(), "<br/>";
        }
        if (strstr($query, ":") == FALSE) {
            return $this->connection->query($query);
        } else {

            $this->prepare = $this->connection->prepare($query);
        }
    }

    public function execute_query($valarg = array()) {

        try {
            if (empty($valarg)) {

                throw new Exception("There are no values in the execute query function");
                return false;
            }
            if (is_array($valarg) == false) {

                throw new Exception("The values inserted are not in an array");
                return false;
            } else {

                $query = $this->query;
                $paramkeys = array();
                $paramArr = array();

                if (strstr($query, ":")) {


                    preg_match_all("/:(w+)/", $query, $paramkeys);

                    $paramArr = array_combine($paramkeys[0], $valarg);


                    $this->prepare->execute($paramArr);
                }
            }
        } catch (Exception $e) {
            echo 'Caught exception: ', $e->getMessage(), "<br/>";
        }
    }

    public function fetch_query() {

        try {
            if($this->execute_query() == false)    {

                 throw new Exception("Sorry you need to fix this first");
            }

             if($this->query() == false)    {

                 throw new Exception("Sorry you need to fix this first");
            }
            else    {

                 $result = $this->prepare->fetch(PDO::FETCH_ASSOC);

                return $result;
            }
        }
        catch (Exception $e) {
            echo 'Caught exception: ', $e->getMessage(), "<br/>";
        }


    }

}

?>