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SQL Identity column changed

I have an ERP database where all tables have an identity field column. It appears that on one of the tables someone changed the characteristic of this column to not be identity. I need to change this column back to being an identity column. This table has data in it. What is the best way to switch it back to being an indentity column?

Habib Pourfard

You can change the column back to identity via Management studio but you can't alter the existing columns for identity.

Assume your table name is 'MyTable', column Name is 'ID' that is primary key and named 'PK_MyTable', one solution is to create a new column with identity and drop the existing column:

ALTER TABLE dbo.MyTable
ADD ID_New INT IDENTITY(1, 1)
Go

ALTER TABLE [dbo].[MyTable] DROP CONSTRAINT [PK_MyTable]
ALTER TABLE MyTable DROP COLUMN ID
Go

EXEC SP_RENAME 'MyTable.ID_New', 'ID', 'Column'

GO
ALTER TABLE [dbo].[MyTable] ADD  CONSTRAINT [PK_MyTable] PRIMARY KEY CLUSTERED 
(
[ID] ASC
)

Open in new window

The above solution is not a good idea if your table is related to other tables, you need to remove and add relations again while the ID_New column regenerates new values.

rwheeler23

ASKER

Therein lies my problem. This table is related to others and when I am done I need this identity column have the same name as when it started. What do you think of this?

copy the entire contents of this table to a back up table
truncate the original table
change the indentity property back to identity
copy the backup table to the original table

ASKER CERTIFIED SOLUTION

Anthony Perkins

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rwheeler23

ASKER

I think was caused this was someone somewhere along the way used integration services and did not pay attention to the fact that it will drop any identity fields by default. You are correct. This should be done in the query window.

I first tried it your way and then mine. Both were successful. Thanks.

rwheeler23

ASKER

Thanks for the tips. Someone can now go off to a New Year's party.