code: func (s *Schema) ColumnsByIndices(offsets []int) []*Column {
  	cols := make([]*Column, 0, len(offsets))
  	for _, offset := range offsets {
  		cols = append(cols, s.Columns[offset])
  	}
  	return cols
  }
docs: // ColumnsByIndices returns columns by multiple offsets.
  // Callers should guarantee that all the offsets provided should be valid, which means offset should:
  // 1. not smaller than 0, and
  // 2. not exceed len(s.Columns)