Getting Multiple Averages

SELECT AVG(answer) as average
	FROM answers
	INNER JOIN questions ON answers.question_id = questions.question_id
	INNER JOIN categories ON categories.category_id = questions.category_id
	WHERE categories.category_id = 2");

SELECT AVG(answer) as average
	FROM answers
	INNER JOIN questions ON answers.question_id = questions.question_id
	INNER JOIN categories ON categories.category_id = questions.category_id
	WHERE categories.category_id = 2");

SELECT AVG(answer) as average, categories.categoryId 
	FROM answers
	INNER JOIN questions ON answers.question_id = questions.question_id
	INNER JOIN categories ON categories.category_id = questions.category_id
	group by categories.categoryId 
        order by  categories.categoryId 

SELECT categories.category_id
     , AVG(answers.answer) as average
  FROM categories
INNER
  JOIN questions
    ON questions.category_id = categories.category_id
INNER
  JOIN answers
    ON answers.question_id = questions.question_id
GROUP
    BY categories.category_id