Selecting rows that has exactly same data as other table - oracle

Question

I have these tables:
Products, Articles, Product_Articles
Lets say, product_ids are: p1 , p2 article_ids are: a1 , a2 , a3
product_articles is:
(p1,a1)
(p1,a2)
(p2,a1)
(p2,a1)
(p2,a2)
(p2,a3)
How to query for product_id, which has only a1,a2, nothing less, nothing more?

Answer 1

UPDATED Try
SELECT p.*
FROM products p JOIN
(
SELECT product_id
FROM product_articles
GROUP BY product_id
HAVING COUNT(*) = SUM(CASE WHEN article_id IN (1, 2) THEN 1 ELSE 0 END)
AND SUM(CASE WHEN article_id IN (1, 2) THEN 1 ELSE 0 END) = 2
) q ON p.product_id = q.product_id
or
SELECT p.*
FROM products p JOIN
(
SELECT product_id, COUNT(*) a_count
FROM product_articles
WHERE article_id IN (1, 2)
GROUP BY product_id
HAVING COUNT(*) = 2
) a ON p.product_id = a.product_id JOIN
(
SELECT product_id, COUNT(*) total_count
FROM product_articles
GROUP BY product_id
) b ON p.product_id = b.product_id
WHERE a.a_count = b.total_count
Here is SQLFiddle demo for both queries

Answer 2

This is an example of a "set-within-sets" subquery. I advocate using aggregation with a having clause for the logic, because this is the most general way to express the relationships.
The idea is that you can count the appearance of the articles within a product (in this case) in a way similar to using a where statement. The code is a bit more complex, but it offers flexibility. In your case, this would be:
select pa.product_id
from product_articles pa
group by pa.product_id
having sum(case when pa.article_id = 'a1' then 1 else 0 end) > 0 and
sum(case when pa.article_id = 'a2' then 1 else 0 end) > 0 and
sum(case when pa.article_id not in ('a1', 'a2') then 1 else 0 end) = 0;
The first two clauses count the appearance of the two articles, making sure that there is at least one occurrence of each. The last counts the number of rows without those two articles, making sure there are none.
You can see how this easily generalizes to more articles. Or to queries where you have "a1" and "a2" but not "a3". Or where you have three of four of specific articles, and so on.

Answer 3

I believe this can be done entirely using relational joins, as follows:
SELECT DISTINCT pa1.PRODUCT_ID
FROM PRODUCT_ARTICLES pa1
INNER JOIN PRODUCT_ARTICLES pa2
ON (pa2.PRODUCT_ID = pa1.PRODUCT_ID)
LEFT OUTER JOIN (SELECT *
FROM PRODUCT_ARTICLES
WHERE ARTICLE_ID NOT IN (1, 2)) pa3
ON (pa3.PRODUCT_ID = pa1.PRODUCT_ID)
WHERE pa1.ARTICLE_ID = 1 AND
pa2.ARTICLE_ID = 2 AND
pa3.PRODUCT_ID IS NULL
SQLFiddle here.
The inner join looks for products associated with the articles we care about (articles 1 and 2 - produces product 1 and 2). The left outer looks for products associated with articles we don't care about (anything article except 1 and 2) and then only accepts products which don't have any unwanted articles (i.e. pa3.PRODUCT_ID IS NULL, indicating that no row from pa3 was joined in).