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

    public function sum($column)
    {
        $result = $this->aggregate(__FUNCTION__, [$column]);
        return $result ?: 0;
    }

 /**
  * Retrieve the sum of the values of a given column.
  *
  * @param string $column
  * @return float|int 
  * @static 
  */
 public static function sum($column)
 {
     return \Illuminate\Database\Query\Builder::sum($column);
 }