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Persisted vs Non-persisted Computed columns
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Persisted vs Non-persisted Computed columns
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VM-723206
VM-723206
Posted Wednesday, October 06, 2010 9:01 PM
SSChasing Mays
Group: General Forum Members
Last Login: Saturday, April 06, 2013 12:20 AM
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Comments posted to this topic are about the item
Persisted vs Non-persisted Computed columns
Post #1000107
UMG Developer
UMG Developer
Posted Wednesday, October 06, 2010 9:03 PM
SSCrazy
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Nice question, thanks.
Though I think formatting the code into little sections, and including the commented select statements, makes it a little more confusing and harder to read than it could have been.
Post #1000108
SQLRNNR
SQLRNNR
Posted Thursday, October 07, 2010 12:34 AM
SSCoach
Group: General Forum Members
Last Login: Thursday, May 16, 2013 1:46 PM
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Thanks for the question.
Jason
AKA CirqueDeSQLeil
I have given a name to my pain...
MCM SQL Server 2008
SQL RNNR
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Post #1000137
GPO
GPO
Posted Thursday, October 07, 2010 1:50 AM
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Just one question. What's the significance of the (nolock) hint? Could you argue that none of the answers could be guaranteed in the event of a dirty read? Cheers and many thanks for the question.
GPO
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Post #1000170
Ian Elliott
Ian Elliott
Posted Thursday, October 07, 2010 3:56 AM
SSC Veteran
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Argh didn't get it wrong because I didn't know the answer but rather because I can't seem to count this morining.
Post #1000252
Hugo Kornelis
Hugo Kornelis
Posted Thursday, October 07, 2010 4:27 AM
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Nice question, though maybe a bit too easy.
Shame about the (nolock) hints, though. They serve no purpose, and they might lead people to believe that these hints are okay to use. They are not, except in a very limited amount of situations.
Hugo Kornelis, SQL Server MVP
Visit my SQL Server blog:
http://sqlblog.com/blogs/hugo_kornelis
Post #1000274
Koen Verbeeck
Koen Verbeeck
Posted Thursday, October 07, 2010 4:33 AM
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Nice question.
I was afraid it was some trick question of some exotic behaviour of SQL Server (with the no lock hints and everything), but luckily common sense was enough to answer the question.
How to post forum questions.
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Post #1000277
Nils Gustav Stråbø
Nils Gustav Stråbø
Posted Thursday, October 07, 2010 5:31 AM
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Hugo Kornelis (10/7/2010)
and they might lead people to believe that these hints are okay to use. They are not, except in a very limited amount of situations.
You won't believe how many people that actually use NOLOCK or READ_UNCOMMITTED to "fix" concurrency and locking problems. One of our vendors use NOLOCK in every(!) SELECT statement in a system we have purchased from them. They have never bothered to explain the reason for doing it, but my guess, after doing some investigation, is that it is caused by two things:
- Lots of missing indexes, which results in excessive scans
- Bad programming, because when I save data in the front-end, SQL Profiler showed that before the transaction for the update statement was committed, another connection from my pc was opened trying to read the updated row(s).
Post #1000313
sjimmo
sjimmo
Posted Thursday, October 07, 2010 6:17 AM
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First - this was a very good question. Learned something today which is great.
Hugo
Shame about the (nolock) hints, though. They serve no purpose, and they might lead people to believe that these hints are okay to use. They are not, except in a very limited amount of situations.
What would these limited situations be?
Nils
You won't believe how many people that actually use NOLOCK or READ_UNCOMMITTED to "fix" concurrency and locking problems. One of our vendors use NOLOCK in every(!) SELECT statement in a system we have purchased from them. They have never bothered to explain the reason for doing it, but my guess, after doing some investigation, is that it is caused by two things:
- Lots of missing indexes, which results in excessive scans
- Bad programming, because when I save data in the front-end, SQL Profiler showed that before the transaction for the update statement was committed, another connection from my pc was opened trying to read the updated row(s).
How about thousands of connections hitting against high volume OLTP databases that are also required for up to the minute reporting where replication is not an issue nor are dirty reads?
There are times where hints are required. I may not like them as the norm, but I don't think that one should dismiss them all together.
Steve Jimmo
Sr DBA
“If we ever forget that we are One Nation Under God, then we will be a Nation gone under." - Ronald Reagan
Post #1000352
Hugo Kornelis
Hugo Kornelis
Posted Thursday, October 07, 2010 6:39 AM
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sjimmo (10/7/2010)
Hugo
Shame about the (nolock) hints, though. They serve no purpose, and they might lead people to believe that these hints are okay to use. They are not, except in a very limited amount of situations.
What would these limited situations be?
Mostly queries that report aggregated data for an audience that doesn't care about the exact number, but only wants an indication. If the numbers my query produces will be rounded to the nearest million dollars anyway, I can live with a result that might be a couple of thousand dollars off.
Hugo Kornelis, SQL Server MVP
Visit my SQL Server blog:
http://sqlblog.com/blogs/hugo_kornelis
Post #1000374
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