Data aggregation with left-outer join - sql

Question

I am trying to pull some data with transaction counts, by branch, by week, which will later be used to feed some dynamic .Net charts.
I have a calendar table, I have a branch table and I have a transaction table.
Here is my DB info (only relevant columns included):
Branch Table:
ID (int), Branch (varchar)
Calendar Table:
Date (datetime), WeekOfYear(int)
Transaction Table:
Date (datetime), Branch (int), TransactionCount(int)
So, I want to do something like the following:
Select b.Branch, c.WeekOfYear, sum(TransactionCount)
FROM BranchTable b
LEFT OUTER JOIN TransactionTable t
on t.Branch = b.ID
JOIN Calendar c
on t.Date = c.Date
WHERE YEAR(c.Date) = #Year // (SP accepts this parameter)
GROUP BY b.Branch, c.WeekOfYear
Now, this works EXCEPT when a branch doesn't have any transactions for a week, in which case NO RECORD is returned for that branch on that week. What I WANT is to get that branch, that week and "0" for the sum. I tried isnull(sum(TransactionCount), 0) - but that didn't work, either. So I will get the following (making up sums for illustration purposes):
+--------+------------+-----+
| Branch | WeekOfYear | Sum |
+--------+------------+-----+
| 1 | 1 | 25 |
| 2 | 1 | 37 |
| 3 | 1 | 19 |
| 4 | 1 | 0 | //THIS RECORD DOES NOT GET RETURNED, BUT I NEED IT!
| 1 | 2 | 64 |
| 2 | 2 | 34 |
| 3 | 2 | 53 |
| 4 | 2 | 11 |
+--------+------------+-----+
So, why doesn't the left-outer join work? Isn't that supposed to
Any help will be greatly appreciated. Thank you!
EDIT: SAMPLE TABLE DATA:
Branch Table:
+----+---------------+
| ID | Branch |
+----+---------------+
| 1 | First Branch |
| 2 | Second Branch |
| 3 | Third Branch |
| 4 | Fourth Branch |
+----+---------------+
Calendar Table:
+------------+------------+
| Date | WeekOfYear |
+------------+------------+
| 01/01/2015 | 1 |
| 01/02/2015 | 1 |
+------------+------------+
Transaction Table
+------------+--------+--------------+
| Date | Branch | Transactions |
+------------+--------+--------------+
| 01/01/2015 | 1 | 12 |
| 01/01/2015 | 1 | 9 |
| 01/01/2015 | 2 | 4 |
| 01/01/2015 | 2 | 2 |
| 01/01/2015 | 2 | 23 |
| 01/01/2015 | 3 | 42 |
| 01/01/2015 | 3 | 19 |
| 01/01/2015 | 3 | 7 |
+------------+--------+--------------+

Answer 1

If you want to return a query that contains each Branch and each week, then you'll need to first create a full list of that, then use a LEFT JOIN to the transactions to get the count. The code will be similar to:
select bc.Branch,
bc.WeekOfYear,
TotalTransaction = coalesce(sum(t.TransactionCount), 0)
from
(
select b.id, b.branch, c.WeekOfYear, c.date
from branch b
cross join Calendar c
-- if you want to limit the number of rows returned use a WHERE to limit the weeks
-- so far in the year or using the date column
WHERE c.date <= getdate()
and YEAR(c.Date) = #Year // (SP accepts this parameter)
) bc
left join TransactionTable t
on t.Date = bc.Date
and bc.id = t.branch
GROUP BY bc.Branch, bc.WeekOfYear
See Demo
This code will create in your subquery a full list of each branch with each date. Once you have this list, then you can JOIN to the transactions to get your total transaction count and you'd return each date as you want.

Answer 2

Bring in the Calendar before you bring in the transactions:
SELECT b.Branch, c.WeekOfYear, sum(TransactionCount)
FROM BranchTable b
INNER JOIN CalendarTable c ON YEAR(c.Date) = #Year
LEFT JOIN TransactionTable t ON t.Branch = b.ID AND t.Date = c.Date
GROUP BY b.Branch, c.WeekOfYear
ORDER BY c.WeekOfYear, b.Branch