Add test for 1 to n relationship through a middle table

For instance:
- clients table
- inquiry_types table (type values could be "email", "in-person meeting", "phone call")
- inquiries table (with a client_id and inquiry_id foreign keys)
- Clients table is the one to have a materialized view.
- materialized_clients has an inquiry_types column like: "email, phone call"
