protected function createSub($query)
    {
        // If the given query is a Closure, we will execute it while passing in a new
        // query instance to the Closure. This will give the developer a chance to
        // format and work with the query before we cast it to a raw SQL string.
        if ($query instanceof Closure) {
            $callback = $query;

            $callback($query = $this->forSubQuery());
        }

        return $this->parseSub($query);
    }