As 200_success already mentioned, we have previously decided that database schema reviews are on topic. This consensus is from back in 2011 though and it may be beneficial to revisit this decision.
- Database schema reviews are also on-topic for DBA.SE.
- Schemas / Designs are not necessarily code, questions for this sometimes get asked with images of UML-Diagrams or similar.
- Schema / Design reviews require significant explanation of the context. Many posts do not provide enough context to review all aspects of a schema.
- "Design" Questions are generally on-topic, but only if they include real code that's implementing that design. It stands to debate whether DDL or (dumb) Data Structures (JSON, PO(C|J)Os, ...) are actually "code". (note: they are source-code alright. Whether they are semantically meaningful is IMO a different discussion)
Overall the question boils down to where we draw the line in the sand about what's (semantically meaningful) code and what is not. I personally don't consider code that has no purpose other than storing a few values and providing manipulations to these values without any further logic to be semantically meaningful. When code can be generated by an IDE I usually ignore the question...
Alternatively the proposal of 200_success seems appropriate for questions about design that are not meaningfully reviewable.