Get full drilldown of a sparce fact table

Question

I have a transaction fact table and product,time and location as a dimension tables. This fact table is sparse so if no Pizzas sold in January there is no record for Pizza in fact table.

When I drill down by product aggregated results for Pizza which is not in the result. But I want it with 0 values as units_sold = 0.

A solution is to join product table to fact table with a left outer join. Then I can get the desired result.

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• But when I cut with another dimension such as location or time, again those products are missing in the result.

• Outer join provides empty column for other dimensional foreign keys so WHERE clause will remove them again.

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How can I solve the problem? (I use ROLAP)

Use join condition is a good idea as some people answered. But I need more general solution.

For example,

Table1

 person      birth year       death year

 a          1950               2006
 b          1952               2008
 c          1960               2007
 d          1953               1990

I want to get year by year count of the people that born between 1950-1953 and died in 2006-2008.

Like

birth = 1950   death = 2006   count = 1
birth = 1951   death = 2006   count = 0
...

Can we handle this scenario by using join conditions and where conditions appropriately.

Answer 1

You want LEFT JOIN , and then LEFT JOIN again. Then conditions go in the on clause. Something like this:

select . . .
from products p left join
     fact f
     on p.product_id = f.product_id left join
     timedim td
     on f.time_id = td.time_id and
        td.month = 'January'