如何从实现DBO的数据库返回列数据？

I am trying to fetch the 'id' column data from my database. Since the purpose of this is a login, there is only one potential row that is returned for the SQL query I have used. I would like to create a reference ($this->result) for the id of the user so that I can use this later on. At the moment it appears nothing is being retrieved from $this->result = $stmt->fetchColumn(); Does anyone have any suggestions for how I can make this work?

$sql='SELECT id FROM member WHERE username=:var and password=:var2';

            try {
                $stmt = $connection->prepare($sql);
                $stmt->bindParam(":var", $myusername);
                $stmt->bindParam(":var2", $mypassword);
                $stmt->execute();
            } catch(PDOException $ex) {
                echo "An Error occured!";
                some_logging_function($ex->getMessage());
            }
            $this->count = $stmt->rowCount();

            $this->result = $stmt->fetchColumn();