compare suppliers from 2 tables in SQL Oracle - sql

Question

I have 2 tables
in both tables are suppliers with items. In the table supplier_with_awards are suppliers which can deliver an item. for 1 item there could be several suppliers. in the table suppliers_with_incomming_goods are suppliers that actually supply the items. There is a situation that non-awarded supplier supplies an item.
case 1
I need to check if the item is in both tables and pick up only those with different suppliers
case 2
same as case 1 but pick up non-awarded suppliers as well.
my data
CREATE TABLE suppliers_with_awards ( supplier, item ) AS
SELECT 'supplier1', 'item1' FROM DUAL UNION ALL
SELECT 'supplier2', 'item1' FROM DUAL UNION ALL
SELECT 'supplier3', 'item2' FROM DUAL UNION ALL
SELECT 'supplier4', 'item3' FROM DUAL ;
CREATE TABLE suppliers_with_incoming_goods ( supplier, item ) AS
SELECT 'supplier1', 'item1' FROM DUAL UNION ALL
SELECT 'supplier2', 'item1' FROM DUAL UNION ALL
SELECT 'supplier5', 'item2' FROM DUAL UNION ALL
SELECT 'supplier6', 'item4' FROM DUAL ;
with simple join we get for item1 unnecessary combinations supplier1-supplier2 and vica versa but in reality supplier1 got award and supplier1 delivers, the same goes for supplier2. So I used row_number to exclude such cross combo if you have better solution let me know.
with award as (
select supplier, item, row_number() over (partition by item order by supplier) r
from suppliers_with_awards
),
goods as (
select supplier, item, row_number() over (partition by item order by supplier) r
from suppliers_with_incoming_goods
)
select a.supplier,a.item,g.supplier from award a join goods g on a.item=g.item and a.r=g.r and a.supplier<>g.supplier;
SUPPLIER ITEM SUPPLIER
supplier3 item2 supplier5
this query finds the item2 because there are different suppliers as I want (case 1).again if there is better solution for this , please ....
But I need somehow to get the non-awarded supplier6 with item4 as well (case 2)
thanks

Answer 1

The current query may not return all results with inserted different values such as supplier7 and supplier8 for item1 inserted into the table suppliers_with_awards. I don't recommend use analytic function in this case, rather you can convert the query into the following which includes NOT EXISTS. And use UNION ALL, since you may need to return more than two supplier which already should be independently listed each unique one into one seperate line
--# Case 1
WITH item_supplier AS
(
SELECT g.item AS item,
a.supplier AS supplier_a,g.supplier AS supplier_g
FROM suppliers_with_awards a
JOIN suppliers_with_incoming_goods g
ON a.item = g.item
)
SELECT DISTINCT item, supplier_a AS supplier
FROM item_supplier i
WHERE NOT EXISTS ( SELECT 0
FROM item_supplier
WHERE supplier_g = i.supplier_a)
UNION ALL
SELECT DISTINCT item, supplier_g
FROM item_supplier i
WHERE NOT EXISTS ( SELECT 0
FROM item_supplier
WHERE supplier_a = i.supplier_g)
for the second case just convert the INNER JOIN to RIGHT or FULL JOIN, and filter out the NULL values of item and supplier in the main query such as
--# Case 2
WITH item_supplier AS
(
SELECT g.item AS item,
a.supplier AS supplier_a,g.supplier AS supplier_g
FROM suppliers_with_awards a
RIGHT JOIN suppliers_with_incoming_goods g
ON a.item = g.item
), its AS
(
SELECT DISTINCT item, supplier_a as supplier
FROM item_supplier i
WHERE NOT EXISTS ( SELECT 0
FROM item_supplier
WHERE supplier_g = i.supplier_a)
UNION ALL
SELECT DISTINCT item, supplier_g
FROM item_supplier i
WHERE NOT EXISTS ( SELECT 0
FROM item_supplier
WHERE supplier_a = i.supplier_g)
)
SELECT *
FROM its
WHERE item IS NOT NULL
AND supplier IS NOT NULL
Demo