Distinct on id with ordering by possible duplicate names - sql

Question

I have the following requisites for a query:
Needs to ordered on a inner joined table (see from_products_products below),
Allow duplicates names on from_products_products
It cannot return duplicates records on the origin table (distinct on products.id).
The following query will eliminate the duplicate names, which is not desired, as I had to put a distinct on from_products_products.name because of the use in order by:
SELECT DISTINCT ON (from_products_products.name, products.id) "products".* FROM "products"
INNER JOIN "suppliers_plugin_source_products" ON "suppliers_plugin_source_products"."to_product_id" = "products"."id"
INNER JOIN "products" "from_products_products" ON "from_products_products"."id" = "suppliers_plugin_source_products"."from_product_id"
INNER JOIN "suppliers_plugin_source_products" "sources_from_products_products_join" ON "sources_from_products_products_join"."to_product_id" = "products"."id"
INNER JOIN "suppliers_plugin_suppliers" ON "suppliers_plugin_suppliers"."id" = "sources_from_products_products_join"."supplier_id"
WHERE "products"."profile_id" = 45781 AND (("products"."type" IN ('SuppliersPlugin::DistributedProduct') OR "products"."type" IS NULL)) AND (products.archived <> true)
ORDER BY from_products_products.name ASC, products.id
Using GROUP BY has the same effect and also don't remove duplicates;
The original query that gives duplicate products when the INNER JOIN doesn't match any product:
SELECT "products".* FROM "products"
INNER JOIN "suppliers_plugin_source_products" ON "suppliers_plugin_source_products"."to_product_id" = "products"."id"
INNER JOIN "products" "from_products_products" ON "from_products_products"."id" = "suppliers_plugin_source_products"."from_product_id"
INNER JOIN "suppliers_plugin_source_products" "sources_from_products_products_join" ON "sources_from_products_products_join"."to_product_id" = "products"."id"
INNER JOIN "suppliers_plugin_suppliers" ON "suppliers_plugin_suppliers"."id" = "sources_from_products_products_join"."supplier_id"
WHERE "products"."profile_id" = 45781 AND (("products"."type" IN ('SuppliersPlugin::DistributedProduct') OR "products"."type" IS NULL)) AND (products.archived <> true)
ORDER BY from_products_products.name ASC
So, how to overcome this on PostgreSQL?
PS: This is part of open-source software Noosfero-ecosol

Answer 1

Does this do what you want?
with t as (
SELECT DISTINCT ON (products.id) "products".*,
from_products_products.name as from_products_name
FROM "products"
INNER JOIN "suppliers_plugin_source_products" ON "suppliers_plugin_source_products"."to_product_id" = "products"."id"
INNER JOIN "products" "from_products_products" ON "from_products_products"."id" = "suppliers_plugin_source_products"."from_product_id"
INNER JOIN "suppliers_plugin_source_products" "sources_from_products_products_join" ON "sources_from_products_products_join"."to_product_id" = "products"."id"
INNER JOIN "suppliers_plugin_suppliers" ON "suppliers_plugin_suppliers"."id" = "sources_from_products_products_join"."supplier_id"
WHERE "products"."profile_id" = 45781 AND (("products"."type" IN ('SuppliersPlugin::DistributedProduct') OR "products"."type" IS NULL)) AND (products.archived <> true)
ORDER BY products.id
)
select t.*
from t
order by from_products_name
It seems to meet your requirements.
EDIT:
If the above does what you want, I can think of five options:
The above using a CTE.
Basically the same logic, using a subquery.
Using window functions, which is structurally very similar.
Using group by.
Using a where clause for the filtering logic.
Here is the group by method:
SELECT "products".*,
MIN(from_products_products.name) as from_products_name
FROM "products"
INNER JOIN "suppliers_plugin_source_products" ON "suppliers_plugin_source_products"."to_product_id" = "products"."id"
INNER JOIN "products" "from_products_products" ON "from_products_products"."id" = "suppliers_plugin_source_products"."from_product_id"
INNER JOIN "suppliers_plugin_source_products" "sources_from_products_products_join" ON "sources_from_products_products_join"."to_product_id" = "products"."id"
INNER JOIN "suppliers_plugin_suppliers" ON "suppliers_plugin_suppliers"."id" = "sources_from_products_products_join"."supplier_id"
WHERE "products"."profile_id" = 45781 AND (("products"."type" IN ('SuppliersPlugin::DistributedProduct') OR "products"."type" IS NULL)) AND (products.archived <> true)
GROUP BY products.id
ORDER BY from_products_name;
This form depends on products.id being declared as a primary key. Alternatively, you can put all the columns from that table in the group by.

Answer 2

Rewriting (simplifying the aliases) yields:
SELECT p1.*
FROM products p1
INNER JOIN suppliers_plugin_source_products spsp
ON spsp.to_product_id = p1.id
INNER JOIN products p2
ON p2.id = spsp.from_product_id
INNER JOIN suppliers_plugin_source_products spsp2
ON spsp2.to_product_id = p1.id -- <<-- Huh?
INNER JOIN suppliers_plugin_suppliers sps
ON sps.id = spsp2.supplier_id
WHERE p1.profile_id = 45781
AND (p1."type" IN ('SuppliersPlugin::DistributedProduct') OR p1."type" IS NULL)
AND p1.archived <> true
ORDER BY p2.name ASC -- <<-- Huh?
;
The outer query only refers to the product tables p1 and p2.
Assuming that JOINing the "suppliers_plugin_source_products" table twice was unintentional, this can be reduced to:
SELECT p1.*
FROM products p1
JOIN products p2
ON EXISTS (
SELECT * FROM suppliers_plugin_source_products spsp
-- the next line might not be necessary ...
INNER JOIN suppliers_plugin_suppliers sps ON sps.id = spsp.supplier_id
WHERE spsp.to_product_id = p1.id
AND spsp.from_product_id = p2.id
)
WHERE p1.profile_id = 45781
AND (p1."type" IN ('SuppliersPlugin::DistributedProduct') OR p1."type" IS NULL)
AND p1.archived <> true
ORDER BY p2.name ASC
;