code: func CutColumnID(b []byte) (remain []byte, n int64, err error) {
  	if len(b) < 1 {
  		return nil, 0, errors.New("invalid encoded key")
  	}
  	// skip the flag
  	b = b[1:]
  	return DecodeVarint(b)
  }
docs: // CutColumnID cuts the column ID from b.
  // It will return the remains as byte slice and column ID