break down by weeks in SQL Server - sql

Question

Given this query:
DECLARE
#FROM_DT DATETIME,
#TO_DT DATETIME
BEGIN
SET #FROM_DT = '10/01/2009'
SET #TO_DT = DATEADD(DAY,7,#FROM_DT)
--WHILE (#FROM_DT <= '10/01/2010')
WHILE (#TO_DT < '10/01/2010')
BEGIN
SELECT
CONVERT(CHAR(10),#FROM_DT,101) AS FROM_DT,
CONVERT(CHAR(10),DATEADD(DAY,-1,#TO_DT),101) AS TO_DT,
COUNTRY AS CITZ,
COUNT(SUBJECT_KEY) AS PEOPLE
FROM MYTALE
WHERE DATE_DT >=#FROM_DT
AND DATE_DT <#TO_DT
GROUP BY COUNTRY
SET #FROM_DT = DATEADD(DAY,7,#FROM_DT)
SET #TO_DT = DATEADD(DAY, 7,#TO_DT)
END
END
Here are my results:
FROM_DT TO_DT COUNTRY PEOPLE
10/01/2009 10/07/2009 A 2
10/01/2009 10/07/2009 B 1
FROM_DT TO_DT COUNTRY PEOPLE
10/08/2009 10/14/2009 A 1
10/08/2009 10/14/2009 C 2
---to
FROM_DT TO_DT COUNTRY PEOPLE
09/23/2010 09/29/2010 A 1
09/23/2010 09/29/2010 B 3
FROM_DT TO_DT COUNTRY PEOPLE
09/30/2010 10/06/2010 C 13
09/30/2010 10/06/2010 D 1
Question:
Is there a way in SQL that it can write the output like below? (I need to consolidate the data. I could copy and paste them but it's 52 weeks of data. Not a efficient way to do it) Please help. I use SQL Server 2005 & 2008 version.
FROM_DT TO_DT COUNTRY PEOPLE
10/01/2009 10/07/2009 A 2
10/01/2009 10/07/2009 B 1
10/08/2009 10/14/2009 A 1
10/08/2009 10/14/2009 C 2
09/23/2010 09/29/2010 A 1
09/23/2010 09/29/2010 B 3
09/30/2010 10/06/2010 C 13
----
From the query above, i commented the WHILE (#FROM_DT <= '10/01/2010') out and replaced it with WHILE (#TO_DT < '10/01/2010') because I would like to get the data for FY10 only, which the date starts from 10/1/2009 to 9/30/2010. However, the result only up to 9/29/2010, the data from 9/30/2010 is not included. Is something wrong with my query? Please help!

Answer 1

Well, SQL Server has a function called DATEPART which can also give you the WEEK part of a date - something like:
SELECT
DATEPART(WEEK, DATE_DT)
Country AS CITZ,
COUNT(Subject_Key) AS PEOPLE
FROM dbo.MyTable
GROUP BY
Country, DATEPART(WEEK, DATE_DT)
This gives you the numeric week number (but not yet the from_date and to_date).
Or you could leave your basic query alone, but store the results into a temporary table:
CREATE TABLE dbo.tmp_Results(FromDT CHAR(10), ToDT CHAR(10),
Country VARCHAR(100), Count INT)
and then just insert your results into that table for each run:
INSERT INTO dbo.tmp_Results(FromDT, ToDT, Country, Count)
SELECT
CONVERT(CHAR(10),#FROM_DT,101) AS FROM_DT,
CONVERT(CHAR(10),DATEADD(DAY,-1,#TO_DT),101) AS TO_DT,
COUNTRY AS CITZ,
COUNT(SUBJECT_KEY) AS PEOPLE
FROM MYTALE
WHERE DATE_DT >=#FROM_DT
AND DATE_DT <#TO_DT
GROUP BY COUNTRY
and then select from that temp table in the end:
SELECT * FROM dbo.tmp_Results

Answer 2

Recursive CTEs to the rescue! No need for temporary tables anymore since you can generate your set on the fly, and can start the weeks at any date instead of on Monday.
(Danger: Written in notepad. Minor bugs / typos may be present. Right idea, though)
WITH weeks (start, end) AS (
select
#from_dt as start
dateadd(day, 7, #from_dt) as end
UNION
select
dateadd(day, start, 7)
dateadd(day, end, 7)
from
weeks
where
start < #last_dt
)
select
w.start,
w.end,
c.country,
count(c.subject_key)
from
my_table c
join weeks on c.date_dt >= start and c.date_dt < end
group by
start, end, country

Answer 3

You could use a dynamic query with a union clause, but what I would do is create a temporary table and insert your results into it. Then you could select out the data from there and drop the temp table.
Your other option would be to create a table that held on to the from-to dates for your weeks and join on that table instead. This would actually be a preferred way to do it, but you would need to keep that table up to date with all of the dates you need.

Answer 4

An approach from data warehousing would be to create a "Weeks" table with all your possible weeks in it, along with their start and end dates:
Week StartDate EndDate
1 10/01/2009 10/07/2009
2 10/08/2009 10/14/2009
3 10/15/2009 10/21/2009
...
...and then just join to that. You fill the "Weeks" table once, in advance -- you can fill it up to the year 3000 if you want -- and then it's available in your database to do queries like this:
SELECT
StartDate, EndDate, COUNTRY, COUNT(SUBJECT_KEY) AS People
FROM
MYTALE INNER JOIN Weeks ON DATE_DT BETWEEN StartDate AND EndDate
GROUP BY
StartDate, EndDate, Country
This often simplifies complicated queries when you need to do data analysis over a range of dates (and you can pre-build a similar "days" or "months" table.) It can also be faster, assuming you've indexed the tables appropriately. These tables are "time dimensions" in star schema data warehouse parlance.

Answer 5

Try:
DECLARE
#FROM_DT DATETIME,
#TO_DT DATETIME
BEGIN
SET #FROM_DT = '10/01/2009'
SET #TO_DT = DATEADD(DAY,7*53,#FROM_DT)
SELECT
CONVERT(CHAR(10),DATEADD(DAY,7*(WEEKNO),#FROM_DT),101) AS FROM_DT,
CONVERT(CHAR(10),DATEADD(DAY,7*(WEEKNO)+6,#FROM_DT),101) AS TO_DT,
COUNTRY AS CITZ,
COUNT(SUBJECT_KEY) AS PEOPLE
(SELECT M.*, TRUNC(DATEDIFF(DAY,#FROM_DT,DATE_DT)/7) WEEKNO
FROM MYTALE M
WHERE DATE_DT >=#FROM_DT
AND DATE_DT <#TO_DT) SQ
GROUP BY COUNTRY, WEEKNO
END