Question

Grouping + fill empty spaces

Asked by: pmengal

Hello,

Consider this table structure / data :

Column :     Connexions         DateRecorded        
Row1 :           10                         1/1/2007 11:12:45 pm              
Row2 :           11                         1/1/2007 11:17:12 pm              
Row3 :           13                          1/1/2007 11:17:59 pm              
Row4 :           12                         1/1/2007 11:25:11 pm              
Row5 :            11                         1/1/2007 11:26:13 pm              
Row6 :            10                         1/1/2007 11:28:52 pm              
Row7 :            9                         1/1/2007 11:28:59 pm              
Row8 :            8                         1/1/2007 11:41:00 pm              
Row9 :            7                         1/1/2007 11:47:15 pm              

Based on that table, I want to retrieve all the data from 11:12 to 12h00 (the getDate() returns 12:00:00), group by minute to get this :

Column :     Connexions         DateRecorded        
Row1 :           10                         1/1/2007 11:12
Row2 :           10                         1/1/2007 11:13
Row3 :           10                         1/1/2007 11:14
Row4 :           10                         1/1/2007 11:15
Row5 :           10                         1/1/2007 11:16
Row6 :           13                          1/1/2007 11:17
Row7 :           13                          1/1/2007 11:18
Row8 :           13                          1/1/2007 11:19
Row9 :           13                          1/1/2007 11:20
Row10 :           13                          1/1/2007 11:21
Row11 :           13                          1/1/2007 11:22
Row12 :           13                          1/1/2007 11:23
Row13 :           13                          1/1/2007 11:24
Row14 :           12                         1/1/2007 11:25
Row15 :            11                         1/1/2007 11:26
Row16 :            11                         1/1/2007 11:27
Row17 :            10                         1/1/2007 11:28
Row18 :            10                         1/1/2007 11:29
Row19 :            10                         1/1/2007 11:30
Row20 :            10                         1/1/2007 11:31
Row21 :            10                         1/1/2007 11:32
Row22 :            10                         1/1/2007 11:33
Row23 :            10                         1/1/2007 11:34
Row24 :            10                         1/1/2007 11:35
Row25 :            10                         1/1/2007 11:36
Row26 :            10                         1/1/2007 11:37
Row27 :            10                         1/1/2007 11:38
Row28 :            10                         1/1/2007 11:39
Row29 :            10                         1/1/2007 11:40
Row30 :            8                         1/1/2007 11:41
Row31 :            8                         1/1/2007 11:42
Row32 :            8                         1/1/2007 11:43
Row33 :            8                         1/1/2007 11:44
Row34 :            8                         1/1/2007 11:45
Row35 :            8                         1/1/2007 11:46
Row36 :            7                         1/1/2007 11:47

Please note that we do a MAX for grouping, so we keep the MAXIMUM value of the grouped records for the same minute. The complexity is to fill the record for each minute that is not on the table.

If it's not possible with a single SQL query, a stored proc is OK ;)

Thanks!

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Asked On
2006-12-16 at 07:17:31ID22095469
Tags

empty

,

fill

,

space

,

data

,

sql

Topic

MS SQL Server

Participating Experts
3
Points
250
Comments
9

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Answers

 

by: angelIIIPosted on 2006-12-16 at 07:19:35ID: 18151736

you should do that in the client application, there it will be much easier (usually) and much more performant.
I would NOT try to solve that in sql

 

by: pmengalPosted on 2006-12-16 at 09:13:07ID: 18152052

And a stored procedure ?

 

by: angelIIIPosted on 2006-12-16 at 09:21:01ID: 18152064

will be still the same. you would have to do a cursor operation, and this is simply very suboptimal.
in front-end code, you would simply read row by row, and if the "next" read date/hour/minute is not the next expected one, you have to fill in with the same connexions value.

 

by: pmengalPosted on 2006-12-16 at 10:35:24ID: 18152240

You mean client side code is more efficient than doing this and encapsulate this in a stored procedure ? This is the first time I hear that.

 

by: angelIIIPosted on 2006-12-16 at 11:40:21ID: 18152371

yes, that is what I want to say. now, clearly this is true for what you are trying to do here, that does not mean that ANY kind of processing will be more efficient in client side code, usually the procedure is more efficient.
however, a process like this one (filling the holes), is simpler and faster using client code.

 

by: pmengalPosted on 2006-12-16 at 11:56:15ID: 18152403

Ok let's see if somebody has another solution. Since everything use Stored Procedure, it is unacceptable to have an exception for that particular task. We want to retrieve the data and not having to modify it on the business layer. This is why I prefer the stored procedure way.

 

by: nmcdermaidPosted on 2006-12-17 at 19:13:53ID: 18156462

The other way you could do it:

1. Create a table containing every single minute in the day call AllMinutes. It goes from 00:00 to 23:59
2. Use the following SQL to get 'single' metric per minute:

SELECT
MAX(Connexions) As Connections,  
CONVERT(VARCHAR(5),DateRecorded,108) As MinuteRecorded
FROM YourTable
WHERE YEAR(DateRecorded) * 10000 + MONTH(DateRecorded) * 100 + DAY(DateRecorded) = 20070101


Then do an outer join on your 'every single minute' table to get something close:

SELECT M.MinuteRecorded, D.Connections
FROM AllMinutes M
LEFT OUTER JOIN
(
SELECT
MAX(Connexions) As Connections,  
CONVERT(VARCHAR(5),DateRecorded,108) As MinuteRecorded
FROM YourTable
WHERE YEAR(DateRecorded) * 10000 + MONTH(DateRecorded) * 100 + DAY(DateRecorded) = 20070101
) D
ON M.MinuteRecorded = D.MinuteRecorded


Note that:

-The field MinuteRecorded in the table AllMinutes needs be CHAR(5) for this to work.
-The outer join will have NULLS in it - we want to fix this, maybe I'll think of something when I come back from lunch
-This only works for a single day.


 

by: ScottPletcherPosted on 2006-12-18 at 14:09:56ID: 18162108

A temp table should do reasonably well in doing that task; IMO, it could even perform better than sending all details to the client for processing there.  For example, please try code below.



SET NOCOUNT ON
-- generate sample data (in temp table, for testing only)
IF OBJECT_ID('tempdb.dbo.#data') IS NOT NULL
    DROP TABLE #data
CREATE TABLE #data (
      dummy VARCHAR(20),
      connexions INT,
      dateRecorded DATETIME
      )
INSERT INTO #data VALUES('Row1 :' , 10 , '1/1/2007 11:12:45 pm')
INSERT INTO #data VALUES('Row2 :' , 11 , '1/1/2007 11:17:12 pm')
INSERT INTO #data VALUES('Row3 :' , 13 , '1/1/2007 11:17:59 pm')
INSERT INTO #data VALUES('Row4 :' , 12 , '1/1/2007 11:25:11 pm')
INSERT INTO #data VALUES('Row5 :' , 11 , '1/1/2007 11:26:13 pm')
INSERT INTO #data VALUES('Row6 :' , 10 , '1/1/2007 11:28:52 pm')
INSERT INTO #data VALUES('Row7 :' ,  9 , '1/1/2007 11:28:59 pm')
INSERT INTO #data VALUES('Row8 :' ,  8 , '1/1/2007 11:41:00 pm')
INSERT INTO #data VALUES('Row9 :' ,  7 , '1/1/2007 11:47:15 pm')


-- main logic, input

DECLARE @startDate DATETIME
DECLARE @endDate DATETIME

-- set start and end date to capture;
-- modify this code as needed to input/set starting values
SET @startDate = '01/01/2007 11:00:23 pm'
SET @endDate = '01/02/2007 12:00:45 am'      


--**************************************************************************************

-- main logic, processing [code should not need modified]
SET NOCOUNT ON
-- make sure @startDate and @endDate are on an even minute
SET @startDate = CONVERT(VARCHAR(30), @startDate, 100)
SET @endDate = CONVERT(VARCHAR(30), @endDate, 100)

IF OBJECT_ID('tempdb.dbo.#mins') IS NOT NULL
    DROP TABLE #mins
CREATE TABLE #mins (
    dateRecorded DATETIME NOT NULL,
    connexions INT NULL,
    UNIQUE CLUSTERED (dateRecorded, connexions)
      )

WHILE @startDate <= @endDate
BEGIN
    INSERT INTO #mins VALUES(@startDate, NULL)
    SET @startDate = DATEADD(MINUTE, 1, @startDate)
END --WHILE


UPDATE mins
SET connexions = data.MaxConnexions
FROM #mins mins
INNER JOIN (
    SELECT CONVERT(DATETIME, CONVERT(VARCHAR(30), dateRecorded, 100), 100) AS dateRecorded,
        MAX(connexions) AS MaxConnexions
    FROM #data
    GROUP BY CONVERT(DATETIME, CONVERT(VARCHAR(30), dateRecorded, 100), 100)
) AS data ON mins.dateRecorded = data.dateRecorded

UPDATE mins
SET connexions = (
    SELECT connexions
    FROM #mins mins2
    WHERE dateRecorded = (
        SELECT MAX(mins3.dateRecorded)
        FROM #mins mins3
        WHERE mins3.dateRecorded < mins.dateRecorded
        AND mins3.connexions IS NOT NULL ) )
FROM #mins mins
WHERE connexions IS NULL

SET NOCOUNT OFF
SELECT *
FROM #mins

20120131-EE-VQP-002

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