This post discusses how Hasura Remote Joins can be used to join data from a Postgres database with any OpenAPI/Swagger compliant REST API. The example provided demonstrates joining users table data in Postgres with exchange rate data from an OpenAPI service, which is a currency exchange rate API. By adding the OpenAPI service as a Remote Schema using Hasura Console and creating a remote relationship called "currency_rates," it becomes possible to query both sets of data in a single API call. The GraphQL query for this operation includes nested queries from the exchange rate API, which filters the results based on the user's currency.