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Cursor taking long time


Cursor taking long time

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PJ_SQL
PJ_SQL
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Hi All,

This is the code I have which users cursors, I have about 2 million records and this script is reading each row and updating it. Is there any suggestions to this?

Declare @A [varchar](9),
@B [integer],
@SQLexec [varchar](500)

Set @B = 0
Declare Cur1 Cursor
For Select A From dbo.tblname

Open Cur1
Fetch from Cur1 into @A
WHILE @@FETCH_STATUS = 0

Begin
Set @B = @B + 1
Set @SQLexec = 'Update dbo.tblname Set rec_num = '+Cast(@B as varchar)+' from dbo.tblname where A = '+@A
Exec(@SQLexec)

Fetch Next From Cur1 into @A
End

Close Cur1
DEALLOCATE Cur

GO
Luis Cazares
Luis Cazares
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You posted in 2 different forums for 2 different versions, please define which one would you like to consider. The other post is this one: http://www.sqlservercentral.com/Forums/Topic1551281-391-1.aspx

Your code seems to do something as simple as this:

Update dbo.tblname Set
rec_num = 0



If it doesn't satisfy your requirements, check the code you posted.


Luis C.
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Are you seriously taking the advice and code from someone from the internet without testing it? Do you at least understand it? Or can it easily kill your server?


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Lynn Pettis
Lynn Pettis
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Before doing anything I just want to verify that you are actually using SQL Server 2000 (or older).

Cool
Lynn Pettis

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PJ_SQL
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It's 2005.
Luis Cazares
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I suggest that all answers should be posted on the other thread.


Luis C.
General Disclaimer:
Are you seriously taking the advice and code from someone from the internet without testing it? Do you at least understand it? Or can it easily kill your server?


How to post data/code on a forum to get the best help: Option 1 / Option 2
Lynn Pettis
Lynn Pettis
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Agreed. That way we can use the newer features that are not available in SQL Server 2000. Makes things easier.

By the way, to the OP, please don't post to multiple forums as it just fragments any responses you may get in response to your question.

Cool
Lynn Pettis

For better assistance in answering your questions, click here
For tips to get better help with Performance Problems, click here
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Igor Micev
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Do you know that cursors' performance is nearly the same to the set-based statements when they are run on up to about 1000 rows. In your case 2 million rows for a cursor will burn the cpu.
You should find a set-based solution, which is not complex for your case. You can use temp tables or CTEs...

Igor Micev,
My blog: www.igormicev.com
Luis Cazares
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Igor Micev (3/14/2014)
Do you know that cursors' performance is nearly the same to the set-based statements when they are run on up to about 1000 rows.

Not really, it might look that way with small sets of data, but it's mostly perception. A set based query will run several times faster than a cursor in most cases.

You should find a set-based solution, which is not complex for your case. You can use temp tables or CTEs...

Like the ones posted in this thread or the other?


Luis C.
General Disclaimer:
Are you seriously taking the advice and code from someone from the internet without testing it? Do you at least understand it? Or can it easily kill your server?


How to post data/code on a forum to get the best help: Option 1 / Option 2
Igor Micev
Igor Micev
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Luis Cazares (3/14/2014)
Igor Micev (3/14/2014)
Do you know that cursors' performance is nearly the same to the set-based statements when they are run on up to about 1000 rows.

Not really, it might look that way with small sets of data, but it's mostly perception. A set based query will run several times faster than a cursor in most cases.

[/quote]
It depends how many columns you're fetching into the cursor and what operations are then perform. However, for one or two columns and small number of rows I haven't seen significant differences. Once I was making some measures, and found out that number (1000) empiricallyl; but as I say, it depends.
Yes, set-based is faster in any case.

Igor Micev,
My blog: www.igormicev.com
Sean Lange
Sean Lange
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Igor Micev (3/14/2014)
Luis Cazares (3/14/2014)
Igor Micev (3/14/2014)
Do you know that cursors' performance is nearly the same to the set-based statements when they are run on up to about 1000 rows.

Not really, it might look that way with small sets of data, but it's mostly perception. A set based query will run several times faster than a cursor in most cases.


It depends how many columns you're fetching into the cursor and what operations are then perform. However, for one or two columns and small number of rows I haven't seen significant differences. Once I was making some measures, and found out that number (1000) empiricallyl; but as I say, it depends.
Yes, set-based is faster in any case.
[/quote]

It is the small number of rows that concerns me here. We don't generally design new processes against tables with millions of rows but we intend to use them there. And even if the table has only a couple hundred rows today, in the future it can grow to millions. Why write code that is just a time bomb? Your argument sounds like the pleas of somebody who was just asked why they wrote a cursor instead of set based solution. Just do it right the first time and then there is no need to worry about it.

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