Cross Join Query - sql

Question

Rewording my original post for further clarification.
I current have the below tables:
Product_Ref
product_id
product_name
Products
product_id
so_date (date)
total_sales
Calendar
dt (date field, each row representing a single day for the past/next 10 years)
I am looking to produce a report that will tell me the number of products that were sold in the past 6 months (based on SYSDATE) on a daily basis, the report should be every combination of day in the last 6 months against every possible product_id in the format:
Product id | date | total sales
If I assume that there were 0 entries in the products table (i.e no sales) I would still expect a complete report output but instead it would show 6 months of zero'd data i.e.
1 | 2012-01-01 | 0
2 | 2012-01-01 | 0
3 | 2012-01-01 | 0
1 | 2012-01-02 | 0
2 | 2012-01-02 | 0
3 | 2012-01-02 | 0
…
This would assume there were 3 products in the product_reference table - my original query (noted below) was my starter for 10, but not sure where to go from here.
SELECT products.product_id, calendar.dt, products.total_sales
FROM products RIGHT JOIN calendar ON (products.so_date = calendar.dt)
WHERE calendar.dt < SYSDATE AND calendar.dt >= ADD_MONTHS(SYSDATE, -7)+1
ORDER BY calendar.dt ASC, products.product_id DESC;

Answer 1

The clue is in the question - you are looking for a CROSS JOIN.
SELECT products.product_id, calendar.dt, products.total_sales
FROM Product_Ref
CROSS JOIN calendar
LEFT JOIN products ON products.so_date = calendar.dt
AND products.product_id = Product_Ref.product_id
WHERE calendar.dt < SYSDATE AND calendar.dt >= ADD_MONTHS(SYSDATE, -7)+1
ORDER BY calendar.dt ASC, products.product_id DESC;
I was confused at first by your table names where "Product" in fact means "sale" and "Product_Ref" is a product!
This is very similar to an example of the use of CROSS JOIN I once posted here.

Answer 2

As far as I understood, what do you want is to have no result if there were no sales, write?
So, I think you just need to change the RIGHT JOIN to INNER JOIN.
By RIGHT joining, if there were register in the JOIN table and there weren't in the FROM table it will return the data from the JOIN table, with NULL values in the columns refering to the FROM table.
By INNER joining you will have results just if you there were data that match in both tables.
Hope I understood well and it helps.

Answer 3

Assuming your desired output is to match only the products date with those in the calendar table, you should use an INNER JOIN:
SELECT c.dt, p.product_id, p.total_sales
FROM calendar c
INNER JOIN products p on c.dt = p.so_date
WHERE c.dt < SYSDATE and c.dt >= ADD_MONTHS(SYSDATE,-7)+1
ORDER BY c.dt ASC, p.product_id DESC;
A CROSS JOIN would produce results with every combination from your products table and your calendar table and thus not require the use of ON.
--EDIT
See edits below (UNTESTED):
SELECT PR.Product_ID, C.dt, P.TotalSales
FROM Calendar C
CROSS JOIN Product_Ref PR
LEFT JOIN Product P ON P.Product_Id = PR.Product_Id and p.so_date = c.dt
WHERE c.dt < SYSDATE and c.dt >= ADD_MONTHS(SYSDATE,-7)+1
ORDER BY c.dt ASC, p.product_id DESC;
Good luck.