code: func generateSQLSearchInfo(keywords searchKeyword) (sqlParameter string) {
  	numberStr := strings.Join(keywords.number, " & ")
  	wordStr := strings.Join(keywords.words, " & ")
  	var fragments []string
  	for _, v := range []string{numberStr, wordStr} {
  		if v != "" {
  			fragments = append(fragments, v)
  		}
  	}
  	searchStr := strings.Join(fragments, " & ")
  	return searchStr
  }
docs: // generateSQLSearchInfo accepts searchKeyword and join them in a way that can be used in sql