code: func Checksum(ctx context.Context, client kv.Client, kvReq *kv.Request, vars *kv.Variables) (SelectResult, error) {
  	resp := client.Send(ctx, kvReq, vars)
  	if resp == nil {
  		return nil, errors.New("client returns nil response")
  	}
  	result := &selectResult{
  		label:    "checksum",
  		resp:     resp,
  		results:  make(chan resultWithErr, kvReq.Concurrency),
  		closed:   make(chan struct{}),
  		feedback: statistics.NewQueryFeedback(0, nil, 0, false),
  		sqlType:  metrics.LblGeneral,
  	}
  	return result, nil
  }
docs: // Checksum sends a checksum request.