Find duplicate combinations - sql

Question

I need a query to find duplicate combinations in these tables:
AttributeValue:
id | name
------------------
1 | green
2 | blue
3 | red
4 | 100x200
5 | 150x200
Product:
id | name
----------------
1 | Produkt A
ProductAttribute:
id | id_product | price
--------------------------
1 | 1 | 100
2 | 1 | 200
3 | 1 | 100
4 | 1 | 200
5 | 1 | 100
6 | 1 | 200
7 | 1 | 100 -- duplicate combination
8 | 1 | 100 -- duplicate combination
ProductAttributeCombinations:
id_product_attribute | id_attribute
-------------------------------------
1 | 1
1 | 4
2 | 1
2 | 5
3 | 2
3 | 4
4 | 2
4 | 5
5 | 3
5 | 4
6 | 3
6 | 5
7 | 1
7 | 4
8 | 1
8 | 5
I need SQL that creates result like:
id_product | duplicate_attributes
----------------------------------
1 | {7,8}

Answer 1

If I understand correct, 7 is a duplicate of 1 and 8 is a duplicate of 2. As phrased, your question is a bit confusing, because 7 and 8 are not related to each other and the only table of interest is ProductAttributeCombinations.
If this is the case, then one method is to use string aggregation
with combos as (
select id_product_attribute,
string_agg(id_attribute::text, ',' order by id_attribute) as combo
from ProductAttributeCombinations pac
group by id_product_attribute
)
select *
from combos c
where exists (select 1
from combos c2
where c2.id_product_attribute > c.id_product_attribute and
c2.combo = c.combo
);

Answer 2

Your question leaves some room for interpretation. Here is my educated guess:
For each product, return an array of all instances with the same set of attributes as any other instance of the same product with smaller ID.
WITH combo AS (
SELECT id_product, id, array_agg(id_attribute) AS attributes
FROM (
SELECT pa.id_product, pa.id, pac.id_attribute
FROM ProductAttribute pa
JOIN PoductAttributeCombinations pac ON pac.id_product_attribute = pa.id
ORDER BY pa.id_product, pa.id, pac.id_attribute
) sub
GROUP BY 1, 2
)
SELECT id_product, array_agg(id) AS duplicate_attributes
FROM combo c
WHERE EXISTS (
SELECT 1
FROM combo
WHERE id_product = c.id_product
AND attributes = c.attributes
AND id < c.id
)
GROUP BY 1;
Sorting can be inlined into the aggregate function so we don't need a subquery for the sort (like #Gordon already provided). This is shorter, but also typically slower:
WITH combo AS (
SELECT pa.id_product, pa.id
, array_agg(pac.id_attribute ORDER BY pac.id_attribute) AS attributes
FROM ProductAttribute pa
JOIN PoductAttributeCombinations pac ON pac.id_product_attribute = pa.id
GROUP BY 1, 2
)
SELECT ...
This only returns products with duplicate instances.
SQL Fiddle.
Your table names are rather misleading / contradict the rest of your question. Your sample data is not very clear either, only featuring a single product. I assume there are many in your table.
It's also unclear whether you are using double-quoted table names preserving CaMeL-case spelling. I assume: no.