I am unable to understand your question. Provide more details. If you are looking for supported database by Hibernate then have a look at http://www.hibernate.org/80.html.
HQL stands for Hibernate Query Language. It means it can be successfully executed on all supported databases. Other types are native queries means, it can be executed for particular database only. HQL gives portability.
I agree with Vishal - HQL is only concerned with the domain objects that you have mapped out in your configuration, and operates at a higher level of abstraction. The Hibernate Dialect you have specified (be it mysql or postgres) is used to generate the actual sql that gets executed at runtime.