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Cursor


Cursor

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WayneS
WayneS
SSCrazy Eights
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HoustonFirefox (7/6/2010)
I personally hate cursors and try not to use them if at all possible. In keeping with our TSQL roots I submit:

DECLARE @Database VARCHAR(255) 
DECLARE @DBList TABLE (DBName varchar(255), Processed CHAR(1))

-- Populate the in-memory table @DBList with all of the database names
insert @DBList
Select [name] , 'N' from master..sysdatabases
where [name] NOT IN( 'model','master','tempdb','msdb')

--select * from @DBList -- DEBUG: Run this to prove population was successful

-- Grab the first DB name from our in-memory table
While EXISTS (Select top 1 DBName from @DBList where Processed='N' order by DBName)
BEGIN
-- Get the DB Name into the @Database variable
Set @Database = (Select top 1 DBName from @DBList where Processed='N' order by DBName)
-- Do whatever awesome stuff with the database...
print @Database
-- Update the Processed flag to skip this DB on the next WHILE pass. Ever-decreasing list
Update @DBList set Processed='Y' where DBName = @Database
END



Efficient? Nope. Easy to write? Yep! Understandable for the DBA that replaces you? Absolutely!

Hope this helps ;-)

This while loop can be worse than a cursor. What you should be trying to avoid is not cursors, but all looping mechanisms - you need to avoid the WHILE statement compeletely.

Wayne
Microsoft Certified Master: SQL Server 2008
Author - SQL Server T-SQL Recipes
If you can't explain to another person how the code that you're copying from the internet works, then DON'T USE IT on a production system! After all, you will be the one supporting it!
Links: For better assistance in answering your questions, How to ask a question, Performance Problems, Common date/time routines,
CROSS-TABS and PIVOT tables Part 1 & Part 2, Using APPLY Part 1 & Part 2, Splitting Delimited Strings

Jeff Moden
Jeff Moden
SSC Guru
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j-1064772 (7/6/2010)
why not



WHILE (@@FETCH_STATUS = 0)





You could certainly do it that way... I just like to avoid the extra FETCH that requires.

--Jeff Moden

RBAR is pronounced ree-bar and is a Modenism for Row-By-Agonizing-Row.
First step towards the paradigm shift of writing Set Based code:
Stop thinking about what you want to do to a row... think, instead, of what you want to do to a column.
If you think its expensive to hire a professional to do the job, wait until you hire an amateur. -- Red Adair

Helpful Links:
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TheSQLGuru
TheSQLGuru
SSChampion
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Cursors are appropriate for some classes of problems - and metadata operations can be one of them. Use the correct tool for the job.

I am with Jeff that you should not make every table have the same fill factor (although making them all something other than 0 is often an improvement). Best is to analyze fragmentation rates and adjust index fill factors appropriately based on that.

Best,
Kevin G. Boles
SQL Server Consultant
SQL MVP 2007-2012
TheSQLGuru on googles mail service
JPHK
JPHK
Grasshopper
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This is admittedly a niggling question, but in Jeff's sample cursor, he used:

DECLARE Employee_Cursor CURSOR LOCAL FORWARD_ONLY READ_ONLY

If you want the cursor to be FORWARD_ONLY READ_ONLY, why wouldn't you just declare it FAST_FORWARD? What are the intrinsic differences that I'm missing?

Thanks,
~ J
Jeff Moden
Jeff Moden
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You could, indeed. But way back when, someone suggested that FAST FORWARD isn't as fast as naming the options separately. I did a test back then and they were right. I don't know if it's changed with SPs, revision changes, etc, etc.

--Jeff Moden

RBAR is pronounced ree-bar and is a Modenism for Row-By-Agonizing-Row.
First step towards the paradigm shift of writing Set Based code:
Stop thinking about what you want to do to a row... think, instead, of what you want to do to a column.
If you think its expensive to hire a professional to do the job, wait until you hire an amateur. -- Red Adair

Helpful Links:
How to post code problems
How to post performance problems
Forum FAQs
anyoneis
anyoneis
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Group: General Forum Members
Points: 11 Visits: 39
Can you believe it, this is the first DRY cursor example I have ever seen. Repeating all of the parameters in the canonical dual FETCH statements was driving me nuts and I couldn't figure out why everyone was doing it that way.

(Not that I would ever use a cursor... ;-) )

Thanks Jeff!
David
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