The example uses a non-existent MIME type named `example/query` as the request's `Content-Type`. We don't know what the syntax and semantics of queries of `exa

The example uses a non-existent MIME type named `example/query` as the request's `Content-Type`. We don't know what the syntax and semantics of queries of `example/query` type are, and we don't need to know because this is just an example! But the intent is clear that one could have `application/sql`, `application/sparql`, and many other MIME types for representations of queries, and if one where to use one of those then the request body should be valid when interpreted in the context of the request's `Content-Type`. Thus you absolutely could have the full power of SQL, if the server were to support it.