Grouping using report query / Case statement in toplink

Question

I have following tables
1. Student with columns id, gender
2. Subject_Score with columns id, student_id, subject_id, score
To get scores grouped by subject, I am doing
ExpressionBuilder subjScoreBuilder = new ExpressionBuilder();
ReportQuery query = new ReportQuery(SubjectScore.class);
query.addAverage("average-score",subjScoreBuilder.get("score"));
query.addGrouping(subjScoreBuilder.get("subjectId"));
Vector responses = (Vector) serverSession.executeQuery(query);
Float score = (Float) queryResult.get("average-score");
This works fine. It gives avg score per each subject
Now i want both in one query
A) avg score per subject
B) avg score per subject per gender
I want to achive this in one query
I am doing like:
ExpressionBuilder subjScoreBuilder =new ExpressionBuilder(SubjectScore.class);
ExpressionBuilder studentExpBuilder = new ExpressionBuilder(Student.class);
Expression expression = subjScoreBuilder.get("studentid").equal(studentExpBuilder.get("id")));
ReportQuery query = new ReportQuery(SubjectScore.class, expression);
query.addAverage("average-score", subjScoreBuilder.get("score"));
query.addGrouping( subjScoreBuilder.get("subjectId"));
query.addGrouping( studentExpBuilder.get("gender"));
This gives me avg scor per each subject per gender. i.e.
it applies grouping on both subjectId & gender.
This is fine.
But I also want avg score per each subject (group on subject only) in same query.
1. How can we achive it?
2. is there something like Case statement in toplink?      
Thanks a lot for any help.

Answer 1

I believe in SQL you would need two queries to do this directly, so you will need to issue two queries.
You could select the Count and Avg, this would give you all the data need to compute the Avg yourself.
i.e.
(count(male) * avg(male) + count(female) * avg(female)) / (count(male) + count(female))