ODATA is a data protocol that relies on REST, which relies on HTTP/S. It supports XML or the more compact/popular JSON. It works across proxies/routers/firewalls. One can use OAUTH2 or other authentication methods. There is a query language built in. The query language is not SQL, but ODATA’s own language.
ODATA supports INSERT, UPDATE, DELETE, SELECT… and many functions, including things like string functions, geo functions , math functions, etc. Note, the functions are not database functions, they are ODATA functions.
If you’re looking to use REST services to access/use your data in a database, ODATA is definitely worth a look!