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SQL Server Loop and Group By

Posted on 2013-01-30
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Last Modified: 2013-01-31
Hello, Experts.
I want to do following for SQL Server looping.

I have several dates that needs to be broken down to intervals depending on days between.
For example, lets say I have some expired dates

01-01-13
01-15-13
01-30-13
02-02-13
03-15-13
03-22-13


I need that to be broken down into this format
Dates           Condition          Good From                 Group
01-01-13   |    Good      |            N/A            |            1
01-15-13   |    Good      |        01-01-13        |            1
01-30-13   |    Good      |        01-01-13        |            1
02-02-13   |    Good      |            N/A            |            2
02-17-13   |    Good      |        02-17-13        |            2
03-15-13   |    Good      |            N/A            |            3
03-22-13   |    Good      |        03-15-13        |            3

Can you guys help me how to do this in SQL Server 2005?

Thank you in advance!
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Question by:kmc10314
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LVL 92

Expert Comment

by:Patrick Matthews
ID: 38837676
Please clearly and explicitly state the rule(s) to be used in determining the grouping and the value for the 'Good From' column.
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Accepted Solution

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Patrick Matthews earned 500 total points
ID: 38837993
Assuming that:
"Group" is determined by calendar month
Earliest date in a given month has no Good From value

Then this appears to do the trick:

CREATE TABLE SomeTable (Expiry datetime)

INSERT INTO SomeTable (Expiry) VALUES
('01-01-2013'),
('01-15-2013'),
('01-30-2013'),
('02-02-2013'),
('02-17-2013'),
('03-15-2013'),
('03-22-2013')

SELECT t1.Expiry AS Dates, 'Good' AS Condition, 
    CASE WHEN t1.Expiry = x.MinDate THEN NULL ELSE x.MinDate END AS [Good From],
    x.[Group]
FROM SomeTable t1 INNER JOIN
    (SELECT MIN(Expiry) AS MinDate, MAX(Expiry) AS MaxDate,
        ROW_NUMBER() OVER(ORDER BY DATEADD(month, DATEDIFF(month, 0, Expiry), 0)) AS [Group]
    FROM SomeTable
    GROUP BY DATEADD(month, DATEDIFF(month, 0, Expiry), 0)) x ON t1.Expiry >= x.MinDate AND t1.Expiry <= x.MaxDate
ORDER BY t1.Expiry

DROP TABLE SomeTable

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Author Comment

by:kmc10314
ID: 38837994
Only critical point will be starting point.
For example, I used 30 days.

So if the initial starting point was 01-01-13, it will be grouped under 01-01-13 until 01-31-13.
Then it can restart on any date after that.
Let's say if it started on 02-02-13, the grouping will last until 03-04-13.
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Author Comment

by:kmc10314
ID: 38838080
I'll try this tomorrow and see how it works out.
Quick question though.
Would it work if the dates are random?  (i.e. some months may not have dates at all)
0
 
LVL 92

Expert Comment

by:Patrick Matthews
ID: 38839205
You're going to have to add more specifics--and a better example--around that thirty day rule.

As for random dates, my approach will work just fine, so long as the frame of reference is the calendar month.  So, the earliest month automatically gets Group 1, the next earliest Group 2, etc.
0
 

Author Comment

by:kmc10314
ID: 38839896
Hello,
I have tried it and it seems like it's always grouping at 1st of the month.
However, that is not the case for this example.
I did realize I made a mistake on the example above, but the concept should be same.
(Good From date for 2-17-13 should actually be 2-02-13)

Good From Date or the initial date of the group does is not always the 1st of the month.
As you see the, the groups can start on 2nd or 15th of the month.

01-01-13   |    Good      |            N/A            |            1                     -> Good From Date 1
01-15-13   |    Good      |        01-01-13        |            1
01-30-13   |    Good      |        01-01-13        |            1
02-02-13   |    Good      |            N/A            |            2                     -> Good From Date 2
02-17-13   |    Good      |        02-02-13        |            2
03-15-13   |    Good      |            N/A            |            3                     -> Good From Date 3
03-22-13   |    Good      |        03-15-13        |            3
0
 

Author Comment

by:kmc10314
ID: 38839931
NM, it did work.
Thank you for your help!
0
 

Author Comment

by:kmc10314
ID: 38840199
One more question, though
I just realized if the "Good From" Date starts from middle of the month and is stretched to next month, it does not pick up

For example,
03-15-13   |    Good      |            N/A            |            3      
03-22-13   |    Good      |        03-15-13        |            3                  -> Works
04-10-13   |    Good      |        03-15-13        |            3                  -> Does not Work.

Can you help me with this?
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