if err != nil {
			return nil, err
		}

		// Pick output column names
		if expr.As != "" {
			output, err = output.Set(expr.As, v)
		} else if comp, ok := getLastKeypathComponent(expr.Expression); ok {
			output, err = output.Set(comp, v)
		} else {
			output, err = output.Set(fmt.Sprintf("_%d", i+1), v)
		}
		if err != nil {
			return nil, err
		}
	}

	// Update count of records output.