i am using PostgreSQL database.
Here is my problem:
i want to use sql datatime functions like "EXTRACT" with hibernate.
but hibernate seems not to support those functions.
How could i do ?

for Example, here is my sql :
SELECT
EXTRACT(month form TIMESTAMP show_datetime) as month,
count(*) as count
FROM tbl_test
GROUP BY EXTRACT(month form TIMESTAMP show_datetime)

How can i use the sql above in hibernate ?

Well, first, Hibernate uses HQL against objects; not SQL against tables.

How about using the SQL Extension function instead of the database specific function:

SELECT {fn MONTH(o.myDateTime)}, count(*) from MyObject as o GROUP BY {fn MONTH(o.myDateTime)}

I am using {fn.. } but got an error :
16:09:50,982 INFO [STDOUT] net.sf.hibernate.QueryException: undefined alias: {fn [select {fn MONTH(view.firstAlert)}, count(*) from UserView as view group by {fn MONTH(view.firstAlert)}]
at net.sf.hibernate.hql.PathExpressionParser.token(PathExpressionParser.java:103)
at net.sf.hibernate.hql.ParserHelper.parse(ParserHelper.java:29)
at net.sf.hibernate.hql.SelectParser.token(SelectParser.java:170)
at net.sf.hibernate.hql.ClauseParser.token(ClauseParser.java:87)
at net.sf.hibernate.hql.ClauseParser.end(ClauseParser.java:114)
at net.sf.hibernate.hql.PreprocessingParser.end(PreprocessingParser.java:143)
at net.sf.hibernate.hql.ParserHelper.parse(ParserHelper.java:30)
at net.sf.hibernate.hql.QueryTranslator.compile(QueryTranslator.java:149)
......