I'd like to retrieve the class name of a given @RID so I can delete the record. I don't know its class name or wether it's a vertex, an edge or something else. How to do it via SQL or the Java API(both would be equally fine)?
Via SQL you can use
select @class from @Rid
Java
OrientGraph g=new OrientGraph(yourPath);
String _class= g.getElement(new ORecordId(9,0)).getProperty("@class");
Delete record:
Sql
delete from 9:0 unsafe
you can see http://orientdb.com/docs/2.1/SQL-Delete.html
Java
g.getRawGraph().getRecord(new ORecordId(9,0)).delete();