code: func CutIndexKey(key kv.Key, colIDs []int64) (values map[int64][]byte, b []byte, err error) {
  	b = key[prefixLen+idLen:]
  	values = make(map[int64][]byte)
  	for _, id := range colIDs {
  		var val []byte
  		val, b, err = codec.CutOne(b)
  		if err != nil {
  			return nil, nil, errors.Trace(err)
  		}
  		values[id] = val
  	}
  	return
  }
docs: // CutIndexKey cuts encoded index key into colIDs to bytes slices map.
  // The returned value b is the remaining bytes of the key which would be empty if it is unique index or handle data
  // if it is non-unique index.