Solved

SQL Server - Update order by limit

Posted on 2015-02-20
8
250 Views
Last Modified: 2015-03-05
Hi Experts,

With SQL Server, how does one do something like this?

Update tasks set Status=1 WHERE Status=0 ORDER BY otherColumn LIMIT 1

I've seen this done as a with statement with a select- but this doesn't seem to lock the row - and I need to lock the row...

Thanks,
Mike
0
Comment
Question by:thready
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
8 Comments
 
LVL 20

Accepted Solution

by:
Russ Suter earned 334 total points
ID: 40621818
The ORDER BY clause is not valid with an update statement. What exactly are you trying to accomplish?
0
 
LVL 13

Expert Comment

by:LIONKING
ID: 40621823
I'm not familiar with the LIMIT, so I can't help you unless you explain a little further what you're trying to do.
0
 
LVL 1

Author Comment

by:thready
ID: 40621834
I have various machines competing to mark N rows in tasks as reserved (as well as their machine name).  I'm trying to avoid collisions because various machines will periodically try to do this...  I guess I need an embedded select statement... but if I do it this way- will I get deadlock errors?
0
Salesforce Made Easy to Use

On-screen guidance at the moment of need enables you & your employees to focus on the core, you can now boost your adoption rates swiftly and simply with one easy tool.

 
LVL 20

Assisted Solution

by:Russ Suter
Russ Suter earned 334 total points
ID: 40621851
I'd be more worried about concurrency errors than deadlock errors. What is your record locking model? Optimistic, pessimistic, other?
0
 
LVL 1

Author Comment

by:thready
ID: 40621873
it's LockReadOnly...  I don't know anything about this, can you explain?
0
 
LVL 1

Author Comment

by:thready
ID: 40621886
I read the docs- I get it- but since it's LockReadonly, I think my problem is with deadlock, not concurrency, right?
0
 
LVL 32

Assisted Solution

by:Daniel Wilson
Daniel Wilson earned 166 total points
ID: 40622227
That syntax is really close to what MySQL supports, but MS SQL Server doesn't.  If your WITH clause gets it for you, good.

Otherwise you may need a stored procedure.

create procedure SetStatus
AS
Begin
 declare @ID int
 Set @ID = (Select top 1 ID from tasks where Status = 0 ORDER BY otherColumn)
 Update tasks set Status=1 WHERE ID=@ID
END

Open in new window


The procedure makes it a transaction which, I think, will take care of your concurrency issues.
0
 
LVL 1

Author Closing Comment

by:thready
ID: 40648442
Thanks everyone
0

Featured Post

Get MySQL database support online, now!

At Percona’s web store you can order your MySQL database support needs in minutes. No hassles, no fuss, just pick and click. Pay online with a credit card.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

The Delta outage: 650 cancelled flights, more than 1200 delayed flights, thousands of frustrated customers, tens of millions of dollars in damages – plus untold reputational damage to one of the world’s most trusted airlines. All due to a catastroph…
For both online and offline retail, the cross-channel business is the most recent pattern in the B2C trade space.
Viewers will learn how the fundamental information of how to create a table.
Viewers will learn how to use the UPDATE and DELETE statements to change or remove existing data from their tables. Make a table: Update a specific column given a specific row using the UPDATE statement: Remove a set of values using the DELETE s…

627 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question