set identity insert on

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set identity insert on

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Sailor

Posted Friday, January 18, 2013 10:02 AM

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I'm doing unicode conversion. I am recreating a mirror image of some 100 databases and all their objects. Before I create the objects, I am changing from varchar to nchar etc. Then I do the copy from the old to new unicode database. If I do an insert with identity insert on and then turn it off, do I need to do a reseed the identities?

Post #1408997

Sean Lange

Posted Friday, January 18, 2013 10:09 AM

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No. This is incredibly easy to evaluate. Create a table and try it out.

create table IdTest
(
	MyId int identity not null,
	SomeValue varchar(10)
)

insert IdTest 
select 'Row 1'

SET IDENTITY_INSERT IdTest on

insert IdTest(MyId, SomeValue)
select 2, 'New Value'

SET IDENTITY_INSERT IdTest off

insert IdTest
select 'Final Test'

Select * from IdTest

drop table IdTest

Now unless your identity column is a primary key or has a unique index there is nothing to prevent duplicates.

You can read about the Set IDENTITY_INSERT on BOL. http://msdn.microsoft.com/en-us/library/ms188059.aspx

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Post #1409002

Vedran Kesegic

Posted Saturday, January 19, 2013 7:44 PM

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How do you copy the data?
With BCP OUT you can dump all tables into files (use -N option to convert all textual fields to unicode while keeping other fields native), and then bulk-load them with BCP IN.
Speed i get on my laptop is about 200 000 rows per second for both directions.
BCP also has -E option to preserve identity value: kind of automatic set identity insert on ... off for you.
HTH,
Vedran

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Post #1409247

ScottPletcher

Posted Monday, January 21, 2013 2:24 PM

Ten Centuries

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No, you should not have to; the db engine takes care of that itself.

From Books Online:
"
If the value inserted is larger than the current identity value for the table, SQL Server automatically uses the new inserted value as the current identity value.
"

So, SQL Server auto-adjusts the identity value up as you add higher-valued rows.

SQL DBA,SQL Server MVP('07, '08, '09)
One man with courage makes a majority. Andrew Jackson

Post #1409714

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