Group by in JPA - jpa

Question

My Question is why the GROUP BY didn't show in the glassfish logs.
i added the following data below because someone wants to see it
public List<Message> listAllMessageBySender(String currentUserID) {
EntityManagerFactory emf = Persistence.createEntityManagerFactory("PersistenceUnit");
EntityManager entityManager = emf.createEntityManager();
TypedQuery<Message> eq = entityManager.createQuery("SELECT m FROM Message m WHERE m.sendBy.userId = :userid GROUP BY m.sendTo.userId", Message.class);
eq.setParameter("userid", Integer.parseInt(currentUserID));
List<Message> message = eq.getResultList();
return message;
}
Glassfish 3.1.2.Logs
FINE: SELECT id, message, send_date, send_by, send_to FROM message WHERE (send_by = ?)
bind => [50]
Data:
User A : sendBy.userId = 50
User B : sendTo.userId = 44
User C : sendTo.userId = 43
id send_date send_by send_to message
1 2013-03-14 14:58:46 44 50 50 send message to 44
2 2013-03-14 14:58:46 50 44 reply from 44 to 50
3 2013-03-14 17:38:52 44 50 2nd reply to 50
6 2013-03-14 18:22:10 50 44 44 reply to 50
7 2013-03-14 18:22:10 50 43 new
in the query above is i want to list all the user sent from User A. it causes duplication because there is two send_to 44. the xhtml below shows :
<ui:repeat value="#{messageController.items}" var="messageItem">
<br />
<div onclick="loadMessage()">
<h:panelGroup layout="block" >
<p:graphicImage height="50" width="50" value="#{messageItem.sendTo.profilePicture}"/>
</h:panelGroup>
<h:panelGroup layout="block" style="width: 270px;">
<h:outputText value="#{messageItem.sendTo.registerName}"/>
<h:panelGroup layout="block" style="float:right;">
<h:outputText value="#{messageItem.sendDate}" >
<f:convertDateTime pattern="HH:mm"/>
</h:outputText>
</h:panelGroup>
</h:panelGroup>
</div>
<p:remoteCommand name="loadMessageBean" action="#{messageController.loadMessage(messageItem.id)}" /> </ui:repeat>
ERD
User Table Message Table
user_id message_id
register_name send_date
send_to ----> referenced by user_id User Table
send_by ----> referenced by user_id User Table

Answer 1

This request doesn't make sense. group by is used when the select clause contains at least one aggregation function (sum, avg, min, max, etc.). And all the other columns must appear in the group by clause.
So for example, the following query would make sense:
SELECT max(m.length), sender.userId from Message m
inner join m.sendBy sender
GROUP BY sender.userId
It would return, for each message sender, the length of its longest message.
Tell us, with example data, what you would like your query to return.
If you want to get all the distinct users whom user A sent a message to, the query should simply be
select distinct m.sendTo from Message m
where m.sendBy.userId = :userid