suppose A has three or more subclasses: A1, A2,A3...
If I use "from A" I can get all its subclasses, but I wanna
distingish those subclasses and display them in diff format
in a report, I have no idea how.

If I can use " select A1,A2... from A", then it'll be easy for
me to understand and handle those subclasses seperately.
I tried and failed. could tell me how.

you could ...

select from A, then loop over the list results and use instanceof to figure out what subclass it is and act accordingly,

issue a select statement for each subclass individually,

encapsulate the display information in each class so you could just select from A and then call o.display() for each instance, each subclass would know how to display itself.

It doesn't look like what you were trying to do is legal SQL syntax.

Won't work if you use proxy for lazy initialization (see 11.1 of hibernate reference guide)

I try to use seperated "select". now the problem is after I get the result set, I have to split them into diff group according to their status(there is a status field in the table), and display the result set grouped by status. I wonder how to map the table so that I needn't manually group the resultset.

the report is like the following