This week's book giveaway is in the OCMJEA forum. We're giving away four copies of OCM Java EE 6 Enterprise Architect Exam Guide and have Paul Allen & Joseph Bambara on-line! See this thread for details.
hql translates these into meaningful sql functions based on the dialect.
now, there are many scenarios where a database vendor (like oracle) would have created different functions which are not a part of the hql's expression, in those cases, you'd have to use the SQL function name directly in the HQL (jut like you created an SqlRestriction..
if you want to ensure that you don't use any db vendor specific functions you can always load data & work with it afterwards.. or you can create a database view & do all the activities there....