func (o *ObjectKey) keyString() string {
	if o.Lit != nil {
		return string(*o.Lit)
	}
	return o.ID.String()
}

// getLastKeypathComponent checks if the given expression is a path
// expression, and if so extracts the last dot separated component of
// the path. Otherwise it returns false.
func getLastKeypathComponent(e *Expression) (string, bool) {
	if len(e.And) > 1 ||
		len(e.And[0].Condition) > 1 ||
		e.And[0].Condition[0].Not != nil ||

		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
		}
	}