How to Add Identity to the Column in SQL Server

Adding an identity to an existing column

You can't alter the existing columns for identity.

You have 2 options,

1. Create a new table with identity & drop the existing table

2. Create a new column with identity & drop the existing column

Approach 1. (New table) Here you can retain the existing data values on the newly created identity column. Note that you will lose all data if 'if not exists' is not satisfied, so make sure you put the condition on the drop as well!

CREATE TABLE dbo.Tmp_Names
    (
      Id int NOT NULL
             IDENTITY(1, 1),
      Name varchar(50) NULL
    )
ON  [PRIMARY]
go

SET IDENTITY_INSERT dbo.Tmp_Names ON
go

IF EXISTS ( SELECT  *
            FROM    dbo.Names ) 
    INSERT  INTO dbo.Tmp_Names ( Id, Name )
            SELECT  Id,
                    Name
            FROM    dbo.Names TABLOCKX
go

SET IDENTITY_INSERT dbo.Tmp_Names OFF
go

DROP TABLE dbo.Names
go

Exec sp_rename 'Tmp_Names', 'Names'

Approach 2 (New column) You can’t retain the existing data values on the newly created identity column, The identity column will hold the sequence of number.

Alter Table Names
Add Id_new Int Identity(1, 1)
Go

Alter Table Names Drop Column ID
Go

Exec sp_rename 'Names.Id_new', 'ID', 'Column'

See the following Microsoft SQL Server Forum post for more details:

How to alter column to identity(1,1)

How to add Identity Column in SQL server?

You can only have 1 Identity Column per Table. So if you don't have one already, Just alter the table and add the Column. Like this

ALTER TABLE YourTableName
ADD IdCol INT IDENTITY(1,1)

How to add identity to the column in SQL Server?

Okay. I was able to add identity to the existing primary column with 10 million records. Took me about 30 mins.

The steps:

1. Change database to single user mode (to make sure no other connections to databse, can cause lock)

2. Open table in designer mode

3. Make change. Do not save

4. Click Generate Change Script button (usually on the left right above the Object Explorer)

5. Copy generated script
6. Close designer window (you can run only one instance at the time)
7. Open new window

8. Execute script

9. Done. Now your column has identity :)

SQL Server: how to add new identity column and populate column with ids?

Just do it like this:

ALTER TABLE dbo.YourTable
ADD ID INT IDENTITY(1,1)

and the column will be created and automatically populated with the integer values (as Aaron Bertrand points out in his comment - you don't have any control over which row gets what value - SQL Server handles that on its own and you cannot influence it. But all rows will get a valid int value - there won't be any NULL or duplicate values).

Next, set it as primary key:

ALTER TABLE dbo.YourTable
ADD CONSTRAINT PK_YourTable PRIMARY KEY(ID)

Convert an existing Column to Identity

As you are using SQL Server 2012, another possible alternative could be to create a sequence object that has a starting value of the highest ID +1 already in your table, then create a default constraint for your column using GET NEXT VALUE FOR and reference your sequence object you just created.

How to add a new identity column to a table in SQL Server?

you can use -

alter table <mytable> add ident INT IDENTITY

This adds ident column to your table and adds data starting from 1 and incrementing by 1.

To add clustered index -

CREATE CLUSTERED INDEX <indexName> on <mytable>(ident) 

How to update Identity Column in SQL Server?

You can not update identity column.

SQL Server does not allow to update the identity column unlike what you can do with other columns with an update statement.

Although there are some alternatives to achieve a similar kind of requirement.

• When Identity column value needs to be updated for new records

Use DBCC CHECKIDENT which checks the current identity value for the table and if it's needed, changes the identity value.

DBCC CHECKIDENT('tableName', RESEED, NEW_RESEED_VALUE)

• When Identity column value needs to be updated for existing records

Use IDENTITY_INSERT which allows explicit values to be inserted into the identity column of a table.

SET IDENTITY_INSERT YourTable {ON|OFF}

Example:

-- Set Identity insert on so that value can be inserted into this column
SET IDENTITY_INSERT YourTable ON
GO
-- Insert the record which you want to update with new value in the identity column
INSERT INTO YourTable(IdentityCol, otherCol) VALUES(13,'myValue')
GO
-- Delete the old row of which you have inserted a copy (above) (make sure about FK's)
DELETE FROM YourTable WHERE ID=3
GO
--Now set the idenetity_insert OFF to back to the previous track
SET IDENTITY_INSERT YourTable OFF

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