Class extend problem php5/mysql

Jeg har et lille problem. Jeg skal foretage et databaseudtræk ved hjælp af to class's: 1 for database connection og en for min SQL-query men kan ikke få skidtet til at virke.

Kode:
core.classes.php:

class dbConnect {
    public $conn;

    //Method to connect to our database
    public function __construct($host, $user, $pass, $db) {
        $this->conn = mysqli_connect($host, $user, $pass, $db);
    }
}
class sqlConnect{
    //public $row;
    //Method to select fields or all from our database
    public function selectQuery($table, $id_field, $field, $colum, $where, $callback) {
        if ($where != "") $where = "WHERE $where";
        if ($field == "") $field = "*";
        if ($table == "" || $callback == ""){
        echo "En eller flere parametre mangler i selectQuery.";
        exit();
        }else{
        $result = mysqli_query($this->conn, "SELECT $field FROM $table $where") or die(mysqli_error($this->conn));
        }

        //Lets loop through our rows in our database and then call our function to print the results
        while ($row = mysqli_fetch_array($result)) {
            $callback($row['email'],$row['welcome']);
        }
    }
   
//Function to print out our rows in the database and create a delete/update link
function echoQuery1($value){
    echo "$value";
    }

default.php:
$db = new dbConnect("localhost","root","****","database");
$sql= new sqlConnect();

//Parameters to send back: table name, id_field name, field name, colum name, where clause, function echoQuery1
$sql->selectQuery("site","","","","","echoQuery1");


Nogen ideer?