table joining duplicate records

hi all,

somebody please help me with my sql statement.
or point me to the right documentation that i need to read.

what i want to working on right now is to create a db for a survey app
my tables look this

surveys
survey_id:survey
----------------
1 : survey1

categories
category_id:category
----------------
1 :category1

questions
question_id:question
----------------
1 :question1

answers
answer_id:answer
----------------
1 :answer1
2 :answer2

questions_answers
question_answer_id:survey_id:category_id:question_id:answer_id
1 :1 :1 :1
1 :1 :1 :2

and my query looks like this

select s.survey, c.category, q.question, a.answer from questions_answers
qa, answers a, questions q, categories c, surveys s
where qa.answer_id = a.answer_id and qa.question_id = q.question_id and
qa.category_id = c.category_id and qa.survey_id = s.survey_id;

after executing the code,
i get results like this.

--query results--
survey :category :question :answer
survey1:category1:question1:answer1
survey1:category1:question1:answer2

how can i elimate duplicates on my query results?
an also am i using the right 'table joining' or table design for my
survey app?

any help would be appriciated.
thanks in advance.

--
"A whim, a thought, and more is sought... awake, my mind... thy will be wrought!"