WHERE子句为空数组的PDO SELECT


PDO SELECT with WHERE clause empty array

我正在尝试用PDO进行SELECT。我使用"用户名"列来指定用户信息。当我使用"WHERE id = $user_id"时,它会返回正确的结果,但当我使用"WHERE username = $username"时,它返回一个空数组。这是我的代码

USER MODEL FILE 
class user_model extends Models {
function __construct() {
    parent::__construct();
}
function e_mail_control($e_mail)
{
    $this->db->select('*');
    $this->db->where(array('user_e_mail' => $e_mail));
    return $this->db->get('users', PDO::FETCH_ASSOC);
}
function username_control($username)
{
    $this->db->select('*');
    $this->db->where(array('user_username' => $username));
    return $this->db->get('users', PDO::FETCH_ASSOC);
}}

您需要对$username:使用单引号

WHERE username = '$username'