code: protected function translateOrderBy() { // @codingStandardsIgnoreLine
  		$build = array();
  
  		foreach ( $this->statements['orders'] as $column => $direction ) {
  
  			// in case a raw value is given we had to
  			// put the column / raw value an direction inside another
  			// array because we cannot make objects to array keys.
  			if ( is_array( $direction ) ) {
  				list( $column, $direction ) = $direction;
  			}
  
  			if ( ! is_null( $direction ) ) {
  				$column .= ' ' . $direction;
  			}
  
  			$build[] = $column;
  		}
  		return 'order by ' . join( ', ', $build );
  	}
docs: Build the order by statement
  
  @return string