validate that if a subquery it exists, it and any further subqueries are all part of the same plan.

validateSubquerySamePlan.go

func validateSubquerySamePlan(node sqlparser.SQLNode, outer *engine.Route, vschema VSchema) bool {
	samePlan := true
	inSubQuery := false

	_ = sqlparser.Walk(func(node sqlparser.SQLNode) (kontinue bool, err error) {
		if _, ok := node.(*sqlparser.Subquery); ok {
			inSubQuery = true
			return true, nil
		}

		if !inSubQuery {
			return true, nil
		}

		switch nodeType := node.(type) {
		case *sqlparser.Select:
			bldr, err := processSelect(nodeType, vschema, nil)
			if err != nil {
				return false, err
			}
			innerRoute, ok := bldr.(*route)
			if !ok {
				samePlan = false
				return false, errors.New("dummy")
			}
			if innerRoute.ERoute.Keyspace.Name != outer.Keyspace.Name {
				samePlan = false
				return false, errors.New("dummy")
			}
		case *sqlparser.Union:
			bldr, err := processUnion(nodeType, vschema, nil)
			if err != nil {
				return nil, err
			}
			innerRoute, ok := bldr.(*route)
			if !ok {
				samePlan = false
				return false, errors.New("dummy")
			}
			if innerRoute.ERoute.Keyspace.Name != outer.Keyspace.Name {
				samePlan = false
				return false, errors.New("dummy")
			}
		}

		return true, nil
	}, node)
	return samePlan
}