February 29 comparing to February 28 of previous year - sql

Question

I have a stored procedure that pulls data and joins last year's data on the Date. The problem is that the current year data has nothing to join on because there was no February 29th in 2011. Has anyone else experienced this problem? Anyone have any ideas on how to work around it?
Here is the stored procedure:
SELECT
--b.Date_Rep AS Date_Rep,
SUM(b.AccountsCreatedThisYear) AS AccountsCreatedThisYearTot,
SUM(a.AccountsCreatedThisYear) AS AccountsCreatedLastYearTot,
FROM Report2011.dbo.T_Report_01 b WITH (NOLOCK) --This year
LEFT JOIN Report2011.dbo.T_Report_01 a WITH (NOLOCK) ON DATEADD(yyyy,-1,b.Date_Rep) = a.date_rep --Last year
WHERE (a.Date_Rep BETWEEN DATEADD(year, -1,#StartDate) AND DATEADD(year, -1,#EndDate))

Answer 1

For starters, I wouldn't do a where clause on columns from a table on the outer side of a left join. Try this, instead:
SELECT SUM(b.AccountsCreatedThisYear) AS AccountsCreatedThisYearTot,
SUM(a.AccountsCreatedThisYear) AS AccountsCreatedLastYearTot,
FROM Report2011.dbo.T_Report_01 b WITH (NOLOCK) --This year
LEFT JOIN Report2011.dbo.T_Report_01 a WITH (NOLOCK)
ON DATEADD(yyyy,-1,b.Date_Rep) = a.date_rep --Last year
WHERE b.Date_Rep BETWEEN #StartDate AND #EndDate

Answer 2

Try using a FULL OUTER JOIN instead of a LEFT JOIN and use COALESCE:
SUM(COALESCE(b.AccountsCreatedThisYear, 0)) AS AccountsCreatedThisYearTot and
SUM(COALESCE(a.AccountsCreatedThisYear, 0)) AS AccountsCreatedLastYearTot
so you avoid the NULL's when the dates don't match.

Answer 3

declare #29Feb datetime = convert(datetime,'2012/02/29')
declare #28Feb datetime = convert(datetime,'2012/02/28')
select case when
dateadd(yy,-1,#29Feb) = dateadd(yy,-1,#28Feb)
then 1
else 0 end
This select statement outputs 1, so actually the Feb 29 and Feb 28 dates have only one corresponding date in the past year, Feb 28.
Now you are doing a sum for two periods in different years for which it happens that the first period has 1 day less than the current period.
How would someone answer to the following question:
"How many accounts have been created in the last year's February and how many this year?"
Does it matter the fact one February had 28 days and the other 29? I don't believe so, the reference is February, not the days.
So I see two problems with this query:
There might be a day this year when no accounts have been created, but in the last year, in the same period, some accounts did, so the left join doesn't catch the ones in the last year
For this year for two different dates, 28 and 29 correspond only one day, 28 so this one is summed twice.
SELECT (SUM(b.AccountsCreatedThisYear)
FROM Report2011.dbo.T_Report_01 WITH (NOLOCK) --This year
WHERE Date_Rep BETWEEN #StartDate and #EndDate ) as AccountsCreatedThisYearTot,
(SUM(b.AccountsCreatedThisYear)
FROM Report2011.dbo.T_Report_01 WITH (NOLOCK) -- Last Year
WHERE Date_Rep BETWEEN DATEADD(year, -1,#StartDate) AND DATEADD(year, -1,#EndDate)) as AccountsCreatedLastYearTot

Answer 4

There was no Feb 29 last year but March 1 was 365 days ago and Feb 28 was 366 days ago.
SELECT SUM(b.AccountsCreatedThisYear) AS AccountsCreatedThisYearTot,
SUM(a.AccountsCreatedThisYear) AS AccountsCreatedLastYearTot,
FROM Report2011.dbo.T_Report_01 b WITH (NOLOCK) --This year
LEFT JOIN Report2011.dbo.T_Report_01 a WITH (NOLOCK)
ON DATEADD(dd,-365,b.Date_Rep) = a.date_rep --Last year
WHERE b.Date_Rep BETWEEN #StartDate AND #EndDate
+1 Mark Bannister as I used his syntax