code: public function select( $fields = '' ) {
  		if ( empty( $fields ) ) {
  			return $this;
  		}
  
  		if ( is_string( $fields ) ) {
  			$this->statements['select'][] = $fields;
  			return $this;
  		}
  
  		foreach ( $fields as $key => $field ) {
  			if ( is_string( $key ) ) {
  				$this->statements['select'][] = "$key as $field";
  			} else {
  				$this->statements['select'][] = $field;
  			}
  		}
  
  		return $this;
  	}
docs: Set the selected fields
  
  @param array $fields Fields to select.
  
  @return self The current query builder.