Update - Self Join and Group By

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Update - Self Join and Group By

Author

Topic

Brittney10
Posting Yak Master

154 Posts

Posted - 2012-12-28 : 11:43:29

Below is an example record set:

ID_____Date________Value____Assoc
123____12/28/2012____0_______1
123____12/27/2012____0_______1
123____12/26/2012____0_______2
123____12/25/2012____0_______2

What I need to be able to do is update [Value] to 2 when [Date] is the most recent per [Assoc]. So in the above query, record #1 and record #3 would both be updated. (Grouping by ID and Assoc)

Desired Result set:
ID_____Date________Value____Assoc
123____12/28/2012____2_______1
123____12/27/2012____0_______1
123____12/26/2012____2_______2
123____12/25/2012____0_______2

Thanks for the help ahead of time.

sodeep
Master Smack Fu Yak Hacker

7174 Posts

Posted - 2012-12-28 : 11:54:53

[code]Update T
Set T.Value = Isnull(2,0)
from
(
Select *,DENSE_RANK() OVER(PARTITION BY ID,Assoc Order by Date desc) as Seq
from Table
)T
Where T.Seq = 1[/code]

Brittney10
Posting Yak Master

154 Posts

Posted - 2012-12-28 : 12:33:12

That works great! Thank you. But now I have another problem. I have duplicate records, so I need to update the one who has the most recent identity value. How do I add that logic?

sodeep
Master Smack Fu Yak Hacker

7174 Posts

Posted - 2012-12-28 : 12:47:22

[code]Update T
Set T.Value = 2
from
(
Select *,DENSE_RANK() OVER(PARTITION BY ID Order by Date desc) as Seq
from Table
)T
Where T.Seq = 1[/code]

Brittney10
Posting Yak Master

154 Posts

Posted - 2012-12-28 : 15:01:00

That doesn't quite work because I still need to partition by ID and Assoc.

quote:

Originally posted by sodeep

Update T
Set T.Value = 2
from
(
Select *,DENSE_RANK() OVER(PARTITION BY ID Order by Date desc) as Seq
from Table
)T
Where T.Seq = 1

sodeep
Master Smack Fu Yak Hacker

7174 Posts

Posted - 2012-12-28 : 15:18:46

Do you have Primary key with identity? or explain what you mean by this "I need to update the one who has the most recent identity value"

Brittney10
Posting Yak Master

154 Posts

Posted - 2012-12-28 : 16:08:25

Identity____ID_____Date________Value____Assoc
1___________123____12/28/2012____0_______1
2___________123____12/28/2012____0_______1
3___________123____12/27/2012____0_______2
4___________123____12/27/2012____0_______2

Since I have duplicate records, I need to update the record with the most recent Identity (auto incrementing) column. So record #2 and #4 would be updated. The code you gave me works perfect, except [Value] can only be = 2 once per ID and Assoc. I hope that makes more sense. Thanks for the help!

sodeep
Master Smack Fu Yak Hacker

7174 Posts

Posted - 2012-12-28 : 16:18:52

Ok then do this

Update T
Set T.Value = 2
from
(
Select *,DENSE_RANK() OVER(PARTITION BY ID Order by Date desc,<Your Identity Column> desc) as Seq
from Table
)T
Where T.Seq = 1

Brittney10
Posting Yak Master

154 Posts

Posted - 2012-12-28 : 16:20:56

Perfect! I swear I tried that! Perhaps I was doing "Order By Date, Identity desc". Thank you so much for the help!

quote:

Originally posted by sodeep

Ok then do this

Update T
Set T.Value = 2
from
(
Select *,DENSE_RANK() OVER(PARTITION BY ID Order by Date desc,<Your Identity Column> desc) as Seq
from Table
)T
Where T.Seq = 1

sodeep
Master Smack Fu Yak Hacker

7174 Posts

Posted - 2012-12-28 : 16:21:43

NP. Atleast you learnt now :)

Brittney10
Posting Yak Master

154 Posts

Posted - 2012-12-28 : 16:39:22

I did learn a lot! Thanks for that!

quote:
Originally posted by sodeep

NP. Atleast you learnt now :)

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