Join against date range, aggregate by SUM - sql

Question

I need to gather the SUM of sales made on a certain category item, grouped by day for a selected date range (could be from a week out to 12weeks) and return 0 instead of NULL for days where no transactions have occurred.
My original idea was to use a pre-populated table called "calendar" (shown below) which has about 10yrs of dates which I could LEFT JOIN my "products" table against to get days when no sales occurred as a 0 SUM.
Result was too large to deal with, so I'm trying to first copy the selected range of dates to an empty table called "datetable" which shares the same column names as "calendar". So I have 3 tables:
"calendar" table. It has 10 years worth of dates with following column names:
IsoDate DayNameOfWeek
2012-01-01 Sun
2012-01-02 Mon
2012-01-03 Tue
2012-01-04 Wed
2012-01-05 Thu
2012-01-06 Fri
2012-01-07 Sat
2012-01-08 Sun
2012-01-09 Mon
2012-01-10 Tue
etc for 10yrs
"datetable" table (this is created empty with two columns to prefill from "calendar" table so the date range data for the LEFT JOIN is more compact):
IsoDate DayNameOfWeek
"products" table. It is where I'm storing sales for each ProductCat:
ExpDate ProductCat Amount
2012-01-03 28 232
2012-01-04 29 100
2012-01-04 29 1002
2012-01-06 12 12
2012-01-06 29 9
2012-01-07 10 100
2012-01-07 29 122
2012-01-07 29 17
The output I'm looking for based on a single "ProductCat" number, in this case 29:
IsoDate DayNameOfWeek AmountSummed
2012-01-01 Sun 0
2012-01-02 Mon 0
2012-01-03 Tue 0
2012-01-04 Wed 1102
2012-01-05 Thu 0
2012-01-06 Fri 9
2012-01-07 Sat 139
2012-01-08 Sun 0
2012-01-09 Mon 0
2012-01-10 Tue 0
My code is below. The initial insert works fine but I'm not sure of the syntax that will make the second part with the JOIN and the SUM work:
INSERT INTO datetable (IsoDate, DayNameOfWeek)
SELECT IsoDate, DayNameOfWeek
FROM calendar
WHERE IsoDate
BETWEEN '2012-07-01' AND '2012-07-10'
SELECT ExpDate, SUM(IFNULL(Amount, 0))
AS AmountSummed
FROM products
WHERE ProductCat = 29
AND ExpDate BETWEEN '2012-07-01' AND '2012-07-10'
LEFT JOIN products
ON datetable.IsoDate=products.ExpDate
GROUP BY datetable.IsoDate
EDIT
This is the code that works now:
SELECT C.IsoDate,IFNULL(SUM(P.Amount),0) AS AmountSummed
FROM calendar C LEFT OUTER JOIN products P ON C.IsoDate=P.ExpDate
AND P.ProductCat = 29
WHERE C.IsoDate BETWEEN '2012-07-01' AND '2012-07-10'
GROUP BY C.IsoDate, C.DayNameOfWeek
ORDER BY C.IsoDate

Answer 1

You've pretty much got what you need. However, you don't need the datetable.
Your query should look like this:
SELECT C.IsoDate, C.DayNameOfWeek, IFNULL(SUM(P.Amount),0) AS AmountSummed
FROM calendar C LEFT JOIN products P ON C.IsoDate=P.ExpDate
WHERE C.IsoDate BETWEEN '2012-07-01' AND '2012-07-10'
AND P.ProductCat = 29
GROUP BY C.IsoDate, C.DayNameOfWeek
ORDER BY C.IsoDate
If you really want to use your datetable, just substitute it in for calendar and remove the C.IsoDate BETWEEN '2012-07-01' AND '2012-07-10' (assuming that the datetable was empty before you started) because datetime already has all the date you are looking for.