code: func (q *Query) GroupBy(field string, fields ...string) *Query {
  	if q.RawSQL.Fragment != "" {
  		log(logging.Warn, "Query is setup to use raw SQL")
  		return q
  	}
  	q.groupClauses = append(q.groupClauses, GroupClause{field})
  	if len(fields) > 0 {
  		for i := range fields {
  			q.groupClauses = append(q.groupClauses, GroupClause{fields[i]})
  		}
  	}
  	return q
  }
docs: // GroupBy will append a GROUP BY clause to the query