I think the main conceptual issue here is that we are identifying the "default" zone by name. We should identify it in another unique way, which could be with another table with a FK or with a new column "is_default"
I think the main conceptual issue here is that we are identifying the "default" zone by name. We should identify it in another unique way, which could be with another table with a FK or with a new column "is_default"