Adding documentation and examples for foreign keys

[nielsbrakel]

Hi, I was wondering if it would be a good addition to create foreign keys in the database:

CREATE FOREIGN TABLE stripe.charges (
  id text,
  amount bigint,
  currency text,
  customer text REFERENCES stripe.customers(id), -- added foreign key constraint
  description text,
  invoice text,
  payment_intent text,
  status text,
  created timestamp,
  attrs jsonb
)
  SERVER stripe_server
  OPTIONS (
    object 'charges',
    rowid_column 'id'
  );

My database engineering knowledge is limited so I do not know if this could result in problems down the line, but I think it could help with optimizing query's and maintaining the integrity of the data. Looking forward to hear the pro's and con's. If it is a good idea I can create a PR for this.

[nielsbrakel]

Apperently Postgress does not enforce the key constraints in a foreign table since it does not control the data, so this is not needed :)

Comment from chat GPT:

It's worth noting that a foreign table can still have a primary key defined in PostgreSQL, but the constraint is not enforced in the remote data source, and it may not provide any performance benefits in terms of accessing the data.