oracle, join with special requests - oracle

Question

I have three tables with articles, inventory and warehouse.
CREATE TABLE "ARTICLE"
( "ID" NUMBER(9,0),
"NAME" VARCHAR2(30 BYTE)
)
CREATE TABLE "INVENTORY"
( "ID" NUMBER(9,0),
"ARTICLE_ID" NUMBER(9,0),
"QUANTITY" NUMBER(9,0),
"WAREHOUSE_ID" NUMBER(9,0)
)
CREATE TABLE "WAREHOUSE"
( "ID" NUMBER(9,0),
"NAME" VARCHAR2(30 BYTE)
)
I created a view, with shows me all inventory (with article name, etc.)
CREATE VIEW "INVENTORY_VIEW" AS
a.ID AS A_ID,
a.NAME AS A_NAME,
i.ID AS I_ID,
i.QUANTITY AS I_QUANTITY,
i.WAREHOUSE_ID AS I_WAREHOUSE_ID
FROM
ARTICLE a
LEFT OUTER JOIN INVENTORY i ON i.ARTICLE_ID = a.ID
I did it to make sure, I get a row for each article, even if there's no row in inventory. (I_WAREHOUSE_ID is null in that special case)
This works fine except for one case:
As soon as there is one row in INVENTORY for another warehouse of course the row (with I_WAREHOUSE_ID = null) disapears for the other warehouses.
(The other warehouses (e.g. Warehouse 2) select the inventory by "WHERE I_WAREHOUSE_ID=2" or "I_WAREHOUSE_ID is null".)
Anybody an idea how to solve this?
What I need is a article row for each WAREHOUSE_ID (with ID) if there is no iventory row for this article and warehouse.
My idea was to create a second view with all article / warehouse combinations and then kind of join that table with the inventory, but I had no success.

Answer 1

If I understand you correctly, you want one result row per article and warehouse. So cross join the two tables and outer join the inventory then:
CREATE VIEW inventory_view AS
SELECT
a.id AS article_id,
a.name AS article_name,
i.id AS inventory_id,
i.quantity AS inventory_quantity,
w.id AS warehouse_id
FROM ARTICLE a
CORSS JOIN WAREHOUSE w
LEFT OUTER JOIN inventory i ON i.article_id = a.id AND i.warehouse_id = w.id;

Answer 2

If I understand correctly what you asked (pls next time post expected result in tabular text) you could try following query:
SELECT
A.ID AS A_ID,
A.NAME AS A_NAME,
I.ID AS I_ID,
I.QUANTITY AS I_QUANTITY,
I.WAREHOUSE_ID AS I_WAREHOUSE_ID
, W2.NAME
, W2.ID
FROM ARTICLE A
LEFT JOIN INVENTORY I ON I.ARTICLE_ID = A.ID
CROSS JOIN WAREHOUSE W2
WHERE I.WAREHOUSE_ID IS NULL OR (W2.ID IS NOT NULL AND I.WAREHOUSE_ID=W2.ID);
Sample data:
INSERT INTO ARTICLE VALUES (1,'PROD_A');
INSERT INTO ARTICLE VALUES (2,'PROD_B');
INSERT INTO INVENTORY VALUES (1, 1,10,2);
INSERT INTO "WAREHOUSE" VALUES (1,'WA');
INSERT INTO "WAREHOUSE" VALUES (2,'WB');
Output:
+------+--------+------+------------+----------------+------+----+
| A_ID | A_NAME | I_ID | I_QUANTITY | I_WAREHOUSE_ID | NAME | ID |
+------+--------+------+------------+----------------+------+----+
| 1 | PROD_A | 1 | 10 | 2 | WB | 2 |
| 2 | PROD_B | NULL | NULL | NULL | WA | 1 |
| 2 | PROD_B | NULL | NULL | NULL | WB | 2 |
+------+--------+------+------------+----------------+------+----+