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Is this syntax guaranteed to continue working?


Is this syntax guaranteed to continue working?

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Adi Cohn
Adi Cohn
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Hi all

Pleas check out the code bellow:

declare @tbl table (i int)
declare @i int

insert into @tbl (i) values (1)

update @tbl
set @i = i, i = 2

select @i as varible, i from @tbl



This code stores the column's old value in a variable and then modifies the column's value. I know that code like that has been working for years, but I don't know if it is something that could be modified in the future. If an application has this kind of code, could it break with the next service pack or next SQL Server version or is this kind of code something that should always work?

Adi

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Koen Verbeeck
Koen Verbeeck
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This is known as the all-at-once concept in SQL Server.

All-At-Once Operations

This should continue to work in next versions of SQL Server.


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Eugene Elutin
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Nothing is certain but death and taxes


You should hope that it will work for ever.
Right now, there is nothing in MS BoL which suggests that they might change this bahaviour:
http://msdn.microsoft.com/en-us//library/ms177523.aspx

_____________________________________________
"The only true wisdom is in knowing you know nothing"
"O skol'ko nam otkrytiy chudnyh prevnosit microsofta duh!":-D
(So many miracle inventions provided by MS to us...)

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Adi Cohn
Adi Cohn
SSCrazy Eights
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Thank you for your replies. I appreciate your fast help.

Adi

--------------------------------------------------------------
To know how to ask questions and increase the chances of getting asnwers:
http://www.sqlservercentral.com/articles/Best+Practices/61537/

For better answers on performance questions, click on the following...
http://www.sqlservercentral.com/articles/SQLServerCentral/66909/
Jeff Moden
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Adi Cohn-120898 (7/8/2013)
Hi all

Pleas check out the code bellow:

declare @tbl table (i int)
declare @i int

insert into @tbl (i) values (1)

update @tbl
set @i = i, i = 2

select @i as varible, i from @tbl



This code stores the column's old value in a variable and then modifies the column's value. I know that code like that has been working for years, but I don't know if it is something that could be modified in the future. If an application has this kind of code, could it break with the next service pack or next SQL Server version or is this kind of code something that should always work?

Adi


It sounds like you're scoping out a project, Adi. What do you actually need this for? I ask because what you've posted makes up the "guts" of what has become endearingly known as the "Quirky Update" which, BTW, can also take the form of SET @variable = column = expression when used with some care.

--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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Adi Cohn
Adi Cohn
SSCrazy Eights
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Jeff – Sorry for disappearing, but for some reason I missed your response. What I wanted to do was very simple. I was working on improving performance on a stored procedure. One of the changes that I've made was to make fewer data access statements. In the procedure there was a code that looked like that:


Select @OldValue = Col1 from MyTable where PK=X
Update MyTable SET Col1 = NewValue where PK=X



I wanted to access the table only once instead of twice.
Adi

--------------------------------------------------------------
To know how to ask questions and increase the chances of getting asnwers:
http://www.sqlservercentral.com/articles/Best+Practices/61537/

For better answers on performance questions, click on the following...
http://www.sqlservercentral.com/articles/SQLServerCentral/66909/
Koen Verbeeck
Koen Verbeeck
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Adi Cohn-120898 (7/9/2013)
Jeff – Sorry for disappearing, but for some reason I missed your response. What I wanted to do was very simple. I was working on improving performance on a stored procedure. One of the changes that I've made was to make fewer data access statements. In the procedure there was a code that looked like that:


Select @OldValue = Col1 from MyTable where PK=X
Update MyTable SET Col1 = NewValue where PK=X



I wanted to access the table only once instead of twice.
Adi


You are right to make such an improvement. The old code is not efficient.


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Need an answer? No, you need a question.
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SwePeso
SwePeso
SSCrazy Eights
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Why not use the OUTPUT clause?


N 56°04'39.16"
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Jeff Moden
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Adi Cohn-120898 (7/9/2013)
Jeff – Sorry for disappearing, but for some reason I missed your response. What I wanted to do was very simple. I was working on improving performance on a stored procedure. One of the changes that I've made was to make fewer data access statements. In the procedure there was a code that looked like that:


Select @OldValue = Col1 from MyTable where PK=X
Update MyTable SET Col1 = NewValue where PK=X



I wanted to access the table only once instead of twice.
Adi


The problem with that is that it will only handle one row at a time. I agree that's the way you designed it with the PK=X but what is the larger picture? Is this something that you need to do with a batch of rows?

--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
Adi Cohn
Adi Cohn
SSCrazy Eights
SSCrazy Eights (8.5K reputation)SSCrazy Eights (8.5K reputation)SSCrazy Eights (8.5K reputation)SSCrazy Eights (8.5K reputation)SSCrazy Eights (8.5K reputation)SSCrazy Eights (8.5K reputation)SSCrazy Eights (8.5K reputation)SSCrazy Eights (8.5K reputation)

Group: General Forum Members
Points: 8479 Visits: 6595
Jeff Moden (7/20/2013)
Adi Cohn-120898 (7/9/2013)
Jeff – Sorry for disappearing, but for some reason I missed your response. What I wanted to do was very simple. I was working on improving performance on a stored procedure. One of the changes that I've made was to make fewer data access statements. In the procedure there was a code that looked like that:


Select @OldValue = Col1 from MyTable where PK=X
Update MyTable SET Col1 = NewValue where PK=X



I wanted to access the table only once instead of twice.
Adi


The problem with that is that it will only handle one row at a time. I agree that's the way you designed it with the PK=X but what is the larger picture? Is this something that you need to do with a batch of rows?


It will always be for 1 record. If this would have been with more then few records, I would have used output clause with temporary table.

Adi

--------------------------------------------------------------
To know how to ask questions and increase the chances of getting asnwers:
http://www.sqlservercentral.com/articles/Best+Practices/61537/

For better answers on performance questions, click on the following...
http://www.sqlservercentral.com/articles/SQLServerCentral/66909/
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