please help with query

From: Pornpira Vachareeyanukul <pornpira_at_beta.tricity.wsu.edu>
Date: Tue, 8 Dec 1998 20:42:50 -0800
Message-ID: <Pine.OSF.3.96.981208202251.32731A-100000@beta.tricity.wsu.edu>

Hi
I need some help with the query statement;

table user

ssn               varchar2(9),
first_name        varchar2(20),
last_name         varchar2(20)

table room
room_no           varchar2(10),
teacher_ssn       varchar2(9),

teacher_assistant_ssn varchar2(9)

I'm trying to select all classrooms from room table and get the teacher and teacher assistant first and last name. I'm having the problem writing query so that just in case of there's teacher_ssn in the room table but no ssn in the user table and I can get that room eventhough there's no record of that teacher in the user table.

Here's what I'm trying to do
Select r.room_no, u1.first_name, u1.last_name,

       u2.first_name, u2.last_name
  from room r, user u1, user u2

 where r.teacher_ssn = u1.ssn
   and r.teacher_assistant_ssn = u2.ssn 
 group by r.room_no

;

And I have another question about how to compare 2 counts; I have 2 tables
k_follow which contain msg_id and the follows_id msg_id,
follows_id

and k_group
msg_id
news_id - newsgroup that msg is posted to

Message is posted to various newsgroup and I have to compare if the follow-up message is posted to more newsgroup than the original message. I've been working on it and I've always got error message saying parser error.
Please help me.

Thank you in advance.
Mimi Received on Tue Dec 08 1998 - 22:42:50 CST