Date and filling issues

Hi All,
I'm not quite sure how to phrase this, but essentially my company has me working on some reports and I have some charts associated with the SQL results.

My current query is:

select
transaction_date as date,
sum(sale_amount) as sales
from ej_transaction
where transaction_date
between current_date - Interval '1 month' and current_date
group by transaction_date
order by transaction_date asc

The issue I'm having is that there are some dates where sales of certain items simply don't take place. Instead of putting a date entry in the database with a sale amount of 0, there simply is no entry for that date. I need to make a query that will fill in the dates not found within the date range and populate them with the sales value of 0.

A sample of the current results data would be like
date sales
2008-03-07 100.00
2007-03-10 150.00
2007-03-18 50.00

and what I'm trying to do is fill in the missing dates with sales values of 0.

Thanks,
-CC

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