As part of work to support temporary tables, the system.namespace table is being extended to include an additional ParentSchemaID. This is a step towards supporting additional physical schemas other than public (even though none can be created yet).

Currently, the optimizer assumes that tables can only be created under the public schema and does no permission check. As we add the ability to scope under different schemas, a simple name check is not enough.

Instead, there needs to be a check to see if the schema exists + the user has privileges to create an object under that schema.