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noamg
Posting Yak Master

215 Posts

Posted - 2007-08-27 : 07:06:55

I have this table:

create table History(
PersonId int,
DogID int,
EndTime smalldatetime
)

insert into History( PersonId, DogID, EndTime )
select 12, 44, '2007-08-01'
union
select 12, 45, '2007-08-02'
union
select 12, 46, '2007-08-03'

I need to find who is the previous dog ?
results: PersonId, DogID, PreviousDog:
12, 46, 45
12, 45, 44

thanks
Noam

Noam Graizer

SwePeso
Patron Saint of Lost Yaks

30421 Posts

Posted - 2007-08-27 : 07:11:54

SELECT h.PersonID, h.DogID, (SELECT MAX(p.DogID) FROM History AS p WHERE p.DogID < h.DogID) AS PreviousDogID
FROM History AS h

E 12°55'05.25"
N 56°04'39.16"

SwePeso
Patron Saint of Lost Yaks

30421 Posts

Posted - 2007-08-27 : 07:20:43

SELECT h.PersonID, h.DogID, (SELECT TOP 1 p.DogID FROM History AS p WHERE p.EndTime < h.EndTime ORDER BY p.EndTime DESC) AS PreviousDogID
FROM History AS h

E 12°55'05.25"
N 56°04'39.16"

madhivanan
Premature Yak Congratulator

22864 Posts

Posted - 2007-08-27 : 07:25:45

quote:
Originally posted by Peso

SELECT h.PersonID, h.DogID, (SELECT TOP 1 p.DogID FROM History AS p WHERE p.EndTime < h.EndTime ORDER BY p.EndTime DESC) AS PreviousDogID
FROM History AS h

E 12°55'05.25"
N 56°04'39.16"

I think top in a subquery would be costlier

Madhivanan

Failing to plan is Planning to fail

SwePeso
Patron Saint of Lost Yaks

30421 Posts

Posted - 2007-08-27 : 09:02:28

It depends on what "previous is"...
According to ID? Use first answer
According to DATE? Use second answer.

E 12°55'05.25"
N 56°04'39.16"

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