code: func FindPrefixOfIndex(cols []*Column, idxColIDs []int64) []*Column {
  	retCols := make([]*Column, 0, len(idxColIDs))
  idLoop:
  	for _, id := range idxColIDs {
  		for _, col := range cols {
  			if col.UniqueID == id {
  				retCols = append(retCols, col)
  				continue idLoop
  			}
  		}
  		// If no matching column is found, just return.
  		return retCols
  	}
  	return retCols
  }
docs: // FindPrefixOfIndex will find columns in index by checking the unique id.
  // So it will return at once no matching column is found.