select within a select - how to address nulls

Question

select within a select - how to address nulls

Bullfrog

SSC Eights!

Points: 895
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August 27, 2009 at 10:09 am

#137690

Hi:
I have the following type of table
Col. A Col. B
stop 12:10
start 12:13
stop 12:34
start 12:37
stop 13:03
start 13:09
start 13:13
stop 13:44
start 13:47
....
I want to get to
Col. A Col. B Col. C
stop to start 12:10 12:13
stop to start 12:34 12:37
stop to start 13:03 13:09
stop to start NULL 13:13
stop to start 13:44 13:47
....
I think this a select within a select, but I get stuck when there are two consecutive 'start' in my original record.
Thoughts?
Using SQL Server 2005, Win2003
Thank you!

Viewing 6 posts - 1 through 5 (of 5 total)

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Ron McCullough SSC Guru Points: 63877 More actions · Answer 1

Bullfrog

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If everything seems to be going well, you have obviously overlooked something.

Ron

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matt6288 SSCertifiable Points: 5058 More actions · Answer 2

I chucked this together pretty quick but it works as long as there is always a stop time. If there are consecutive stop times then this blows up. I will try to come back to this if needed.

CREATE TABLE #times ([action] VARCHAR(5), [time] dateTIME)

INSERT INTO #times

SELECT 'stop', '12:10'

UNION ALL

SELECT 'start','12:13'

UNION ALL

SELECT 'stop', '12:34'

UNION ALL

SELECT 'start','12:37'

UNION ALL

SELECT 'stop', '13:03'

UNION ALL

SELECT 'start','13:09'

UNION ALL

SELECT 'start', '13:13'

UNION ALL

SELECT 'stop','13:44'

UNION ALL

SELECT 'start','13:47'

;WITH CTE AS

(

SELECT [action], [time], ROW_NUMBER() OVER (PARTITION BY [action] ORDER BY [time]) AS rowNum FROM #times

)

SELECT 'stop to start' AS [action], NULL AS [stopTime], [time] AS startTime

FROM cte cte1

WHERE [action] = 'start'

AND EXISTS (SELECT * FROM CTE cte2 WHERE cte1.rownum = cte2.rowNum AND cte2.[action] = 'stop' AND cte2.[time] > cte1.[time])

union

SELECT 'stop to start' AS [action], [time], (SELECT MIN([time]) FROM #times b WHERE b.[time] > a.[time] AND b.[action] = 'start')

FROM #times a

WHERE a.[action] = 'stop'

ORDER BY [time]

DROP TABLE #times

drew.allen SSC Guru Points: 76984 More actions · Answer 3

The following works with both multiple start and stop times. It may not be the exact results you want for multiple stop times.

WITH CTE AS

(

SELECT [action], [time], ROW_NUMBER() OVER ( ORDER BY [time] ) AS rowNum FROM #times

)

SELECT a.[action], a.[time], b.[action], b.[time]

FROM CTE AS a

FULL OUTER JOIN CTE AS b

ON a.rowNum = b.rowNum-1

AND a.[action] b.[action]

WHERE IsNull(b.rowNum, 2) > 1

AND IsNull(a.[action], 'stop') = 'stop'

AND IsNull(b.[action], 'start') = 'start'

ORDER BY IsNull(a.[time], b.[time]), b.[time]

Drew

J. Drew Allen
Business Intelligence Analyst
Philadelphia, PA

matt6288 SSCertifiable Points: 5058 More actions · Answer 4

Yep, drew's is much nicer and it handles the logic correctly. I don't even know what I was thinking now that I have read through a much better implementation.

Bullfrog SSC Eights! Points: 895 More actions · Answer 5

Great - thanks a bunch guys!

I never would've figured it out, but now that I see what you did it makes sense.