public function addScalarResult($columnName, $alias, $type = 'string')
    {
        $this->scalarMappings[$columnName] = $alias;
        $this->typeMappings[$columnName]   = $type;

        if ( ! $this->isMixed && $this->fieldMappings) {
            $this->isMixed = true;
        }

        return $this;
    }