Illuminate\Database\Query\Builder::selectSub PHP Method

    public function selectSub($query, $as)
    {
        if ($query instanceof Closure) {
            $callback = $query;
            $callback($query = $this->newQuery());
        }
        if ($query instanceof self) {
            $bindings = $query->getBindings();
            $query = $query->toSql();
        } elseif (is_string($query)) {
            $bindings = [];
        } else {
            throw new InvalidArgumentException();
        }
        return $this->selectRaw('(' . $query . ') as ' . $this->grammar->wrap($as), $bindings);
    }

 /**
  * Add a subselect expression to the query.
  *
  * @param \Closure|\Illuminate\Database\Query\Builder|string $query
  * @param string $as
  * @return \Illuminate\Database\Query\Builder|static 
  * @static 
  */
 public static function selectSub($query, $as)
 {
     return \Illuminate\Database\Query\Builder::selectSub($query, $as);
 }