HSQLDialect does not support the trunc function as part of a SELECT. For example, the following named-query fails:

SELECT TRUNC(myDate) as my_date,
       COUNT(myDate) AS total
FROM com.domain.SomeEntity
GROUP BY TRUNC(startTime) 
ORDER BY TRUNC(startTime)

NOTE: There a truncate function already has been registered in the existing dialect implementation, but it cannot be applied to DATE types.