How can I create a list of weeks in access? - sql

Question

How do I create a query which breaks down a frequency of counts based on a list of weeks between 2 different dates in Access?
At the moment I have the following code in t-sql, but would like to have it run in Access.
declare #fromdate smalldatetime
declare #todate smalldatetime
declare #toptr smalldatetime
declare #fromptr smalldatetime
set #fromdate = '1/11/2010'
set #todate = '27/12/2010'
set #fromptr = dateadd(dd,1 - datepart(weekday,#fromdate), #fromdate)
while #fromptr < #todate
begin
print 'from: ' + cast(#fromptr as nvarchar) + ' --> ' + cast(#toptr as nvarchar)
set #fromptr = dateadd(dd,7, #fromptr)
set #toptr = dateadd(dd,7, #fromptr)
insert into #weeks values (#fromptr, #toptr)
end
I want to somehow bind some rows with lots of dates in them and aggregate them per 'week- ending date' from the dates creating in the table variable. Access doesn't seem to allow this kind of sql query, so was wondering if there was another way of doing this:
1) either by not using an intermediate table at all, 2) and/or converting the above code into access compatible

Answer 1

This will group by week (starting with Sunday) and be faster than other date calculation methods like DateAdd, DateDiff, DatePart, and Format.
SELECT
CDate((([DateColumn] - 1) \ 7) * 7 + 1) AS WeekStartingDate,
Sum([OrderCount]) AS SumOfOrders
FROM
Orders
GROUP BY
CDate((([DateColumn] - 1) \ 7) * 7 + 1);
If you want to see week ending date, add 7 at the end instead of 1. The GROUP BY expression can probably be just ([DateColumn] - 1) \ 7 but I'm not sure.
The backslash performs integer division, dividing by 7 converts a week of dates to a single integer, and the -1 adjusts for the fact that the "zero date" is a Saturday rather than a Sunday. To use a different starting day of the week, adjust the -1 and +1 by the same amount. To use Monday, for example, it would be -2 and +2.
This is language and region independent by depending on VB's internal representation of dates as numbers.

Answer 2

You can use Format in Access queries: http://msdn.microsoft.com/en-us/library/aa159657(v=office.10).aspx
SELECT Format(Date,"ww") FROM Table
GROUP BY Format(Date,"ww")

Answer 3

The plain-vanilla solution is to introduce a Calendar table which may look something like
Calendar
------------------------
FullDate date
CalendarYear integer
DayNumberInWeek integer
DayNumberInMonth integer
DayNumberInYear integer
DayNumberInEpoch integer
WeekNumberInYear integer
WeekNumberInEpoch integer
MonthNumberInYear integer
MonthNumberInEpoch integer
... and many more that you may need to group by
Then if you have table Counters
Counters
-----------
FullDate date
Value integer -- cumulative for one day
You can:
select
WeekNumberInYear
, sum(Value)
from Calendar as a
join Counters as b on b.FullDate = a.FullDate
where CalendarYear = 2010
group by WeekNumberInYear ;
The easiest way to populate the Calendar is to spend some time in Excel, create 10-20 years worth of rows and simply import in a DB.
Nothing specific to Access here, but hope you get the idea.