Getting a variable end of year date and value from MS Access table using SQL - sql

Question

I have some data is that is daily (day on day) closing figures for a tracked supply and is in one MS Access table that has 2 columns - Dates (the date), PXLast(the day's closing figure)).
I have daily data from Jan 1991 to Aug 2013 and I wanted to get the percentage change of PXLast at every year end compared to last year year end as follows:
Year | Percentage Change of PXLast(Year on Year)
1991 | 15.2%
1992 | 9.2%
The year end date varies (not always 31st ) and I am going about getting the last PXLast value by:
1.Get the max date in Dec every year: results in MyYear, MyMonth, MyDay
2.Combine it using DateSerial(MyYear, MyMonth, MyDay)
3.Join the resulting query to the table and inner join on the date column
4.Get the PXLast value
SELECT EndDates.EndDates, NSE20.PX_LAST AS LookPoint
FROM NSE20 INNER JOIN
(SELECT DateSerial([MyYear],[MyMonth],[MyDay])
AS EndDates FROM (SELECT 12 AS MyMonth, MyDay, MyYear FROM
(SELECT Max(Day([Dates])) AS MyDay, Year([Dates]) AS MyYear
FROM NSE20 WHERE (((Month([Dates]))=12))
GROUP BY Year([Dates])) AS EndYearValues)
AS EndValueDates)
AS EndDates ON NSE20.Dates = EndDates.EndDates;
Could anyone assist me get the corresponding value using a query for previous year end
eg for 29 Dec 2006, it should show the current value and show the value for 31 Dec 2005
in the same row ie
Year | Current Year End| Previous Year End
2005 | 3449.00 | 4611.19
2006 | 9.2% |3449.00
Any help is appreciated.
Any suggestions to a better way of doing this is very very welcome....

Answer 1

Let's assume that you have some test data in a table named [NSE20] that looks like this
Dates PXLast
---------- ------
2010-07-01 131
2010-12-31 130
2011-11-12 123
2011-12-30 125
2012-01-03 127
2012-12-31 129
I'd start by creating a saved query in Access named [NSE20_year_ends] that identifies the year-end dates by (calendar) year:
SELECT Year(Dates) AS CalendarYear, Max(Dates) AS YearEndDate
FROM NSE20
GROUP BY Year(Dates)
That will produce
CalendarYear YearEndDate
------------ -----------
2010 2010-12-31
2011 2011-12-30
2012 2012-12-31
Then I'd create another saved query named [NSE20_year_end_balances] to extract the closing balances for each year:
SELECT NSE20_year_ends.CalendarYear, NSE20.PXLast
FROM
NSE20
INNER JOIN
NSE20_year_ends
ON NSE20.Dates = NSE20_year_ends.YearEndDate
That will give us
CalendarYear PXLast
------------ ------
2010 130
2011 125
2012 129
Now we can do a self-join on that query to calculate the percentage change
SELECT
y1.CalendarYear,
(y1.PXLast - y0.PXLast) / y0.PXLast * 100 AS PctChange
FROM
NSE20_year_end_balances y1
INNER JOIN
NSE20_year_end_balances y0
ON y0.CalendarYear = y1.CalendarYear - 1
resulting in
CalendarYear PctChange
------------ -----------------
2011 -3.84615384615385
2012 3.2