How do I show all records from one table for each semi-related record in another?

Question

This problem is extremely difficult to explain and I did not even know how to title it correctly so I do apologise about that in advance.

I have a view of products which is as follows:

Product
ProductId
ProductName

In my database, I have a ratecard table and a ratecard product table. A ratecard may be titled "Tier 1 Customers" and the corresponding RatecardProduct records would be prices for products for that particular ratecard. It may only contain prices for a few products and not all of them.

Ratecard
RatecardId
RatecardName

RatecardProduct
RatecardProductId
RatecardId
ProductId UnitPrice

The problem is that I need to create a view which displays all products for all ratecards. If the ratecard / product combination does not have a corresponding unit price in my ratecardproduct table, it should show NULL or 0.

Imagine I have 10 products and 4 ratecards; the view would contain 40 records, even if the RatecardProduct table was completely empty

The reason I need to do this is because I am populating a gridview on viewing a ratecard and I do not want to have to do a round trip for each row to ascertain if there is a corresponding price.

Thank you so much in advance.

Answer 1

Generate all the rows. Then use left join to bring in the data:

select p.*, r.*, coalesce(rp.unitprice, 0) as unitprice
from products p cross join
     ratecards r left join
     ratecardproduct rp
     on rp.productid = p.productid and rp.ratecardid = r.ratecardid;

Or don't use coalesce() if you want NULL .