Quarterly trending

I have a reporting query that I need to do a quarterly trending on.  A
user enters a begining date and end date, and from there, I have to
determine the closest quarter to it.

Also, the actual Quarter starts on Sept 4th, then add 13 weeks to that,
will be the second quarter.

I was able to do the trending for week/month/year, but I'm stuck on
this quarterly trending.

Any help would be greatly appreciated.

Example of the monthly trending that I have written:

SELECT & #91;VALUE],DATEPART(
MONTH,DATESAMPLE) AS[MONTH]
FROM #TABLE
GROUP BY [VALUE],  DATEPART(MONTH,DATES
AMPLE)
ORDER BY EDIT_SP,  DATEPART(MONTH,DATES
AMPLE)

This would be easy if your business used calendar quarters instead;
can't you make them change? <G>  You could then group by
DATEPART(Quarter, DateSample)

Since that's not likely, a solution might be to use a calendar table
that takes a key Date and maps it to the appropriate quarter, eg:

CREATE TABLE Calendar (DateKey smalldatetime, PeriodQuarter int....
(other columns))

INSERT INTO Calendar (DateKey, PeriodQuarter)
SELECT '9/1/2005', 2
UNION ALL
SELECT '9/4/2005', 3

etc

You could then join and group on the PeriodQuarter value.

Just an idea.
Stu

create a table of the quarters:

CREATE TABLE Quarters
(quarter_name  CHAR(20) NOT NULL PRIMARY KEY,
start_date  DATETIME NOT NULL,
end_date DATETIME NOT NULL,
CHECK (start_date < end_date ));
 

Whatr does thst mean?  give me an algorithm.