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Removing column IDENTITY using T-SQL

Posted on 2004-03-25
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Last Modified: 2011-10-03
What is the T-SQL syntaxe for removing/adding a column identity ?
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Question by:mike_marquet
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Expert Comment

by:Hilaire
ID: 10676981
As far as I know there's no way to add the identity constraint to an existing column
nor to drop the identity constraint
(whithout dropping/recreating)

BUt you can temporarily disable the identity_insert using the following syntax

Disabling Identity insert:
SET IDENTITY_INSERT <Table_Name> ON
GO

enabling Identity insert:
SET IDENTITY_INSERT <Table_Name> OFF
GO
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Expert Comment

by:danblake
ID: 10676994
Try:

ALTER TABLE doc_exe ALTER COLUMN
/* Modify Column_b to have an identity column*/
column_b INT IDENTITY

And the removal is:
ALTER TABLE doc_exe ALTER COLUMN
/* Modify Column_b to have an not have an identity column*/
column_b INT

A slightly bigger question, why do this ?
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Expert Comment

by:Hilaire
ID: 10677042
@dan
Are you sure it works ??
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LVL 13

Expert Comment

by:danblake
ID: 10677054
This code given, is untested.  If there is a way of performing the altering of a column it will be with the ALTER table <table_name> alter column <column_properties> syntax.  I have just had a look at BOL, it does look like Hillare you are right -- it is not yet possible.  

removing/adding a column identity ?
So the only way would be to perform an: (Add identity property:)
alter table doc_exe ADD column_c INT IDENTITY (1,1)

And a remove:
alter table doc_exe DROP column_c


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Author Comment

by:mike_marquet
ID: 10677070
the code given by danblake don't works, I have already try it before !
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by:danblake
ID: 10677079
I wish that it would be possible to redefine a column fully without fully modifying a table at times...but then there are very good reasons why you would not want to do that.
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Author Comment

by:mike_marquet
ID: 10677091
The identity column where I want to remove the identity for can not be delete and reinserted in my case
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Author Comment

by:mike_marquet
ID: 10677102
SQL Enterprise Manager can toggle the identity therefore I think there is way to do it but how ?
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Accepted Solution

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danblake earned 252 total points
ID: 10677142
SQL Enterprise Manager can toggle the identity therefore I think there is way to do it but how ?

The script generated is a complete drop script / rebuild script.

If you click on the Save script button after using EM, you will be able to view the script.
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Assisted Solution

by:Hilaire
Hilaire earned 248 total points
ID: 10677211
SQL EM often generates drop-create statements

To drop an ID column you can

alter table yourtable add newcol int
update yourtable set newcol = oldcol
alter table yourtable drop column oldcol
exec sp_rename 'yourtable.newcol', 'yourtable.oldcol', 'COLUMN'

You'll also have to drop / create indexes, constraints, ... if you have some that use this col

The same can be achieved to create a "new" col with identity using the same logic and the
SET IDENTITY_INSERT <Table_Name> ON / OFF as explained in a previous post


Hilaire


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Expert Comment

by:lguzman1509
ID: 24282957
The only way is to export the data from the identity column to another column with the int datatype, drop the original column and rename de intermediate column.
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