How to set identity column to created table in SQL server - sql-server

Question

I created a table in SQL Server like this:
CREATE TABLE [UserName]
(
[ID] [int] NOT NULL ,
[Name] [nvarchar] (50) NOT NULL ,
[Address] [nvarchar] (200) NULL
CONSTRAINT [PK_UserName] PRIMARY KEY CLUSTERED ([ID] ASC)
) ON [PRIMARY]
GO
If I want to make ID an identity column, what do I need? Do I need to drop and create this table and set ID to [ID] [int] IDENTITY(1,1) NOT NULL .
By using drop and create, all of data from UserName table are lost .
Is there another way to set IDENTITY COLUMN to created table's column without losing data?
I use SQL Server 2008 R2 :)

Answer 1

ALTER TABLE [UserName] DROP COLUMN [ID];
ALTER TABLE [UserName]
ADD [ID] integer identity not null;

Answer 2

Try this one -
DECLARE #temp TABLE
(
ID INT NOT NULL
, Name NVARCHAR(50) NOT NULL
, [Address] NVARCHAR(200) NULL
)
INSERT INTO #temp (ID, Name, [Address])
SELECT ID, Name, [Address]
FROM dbo.UserName
DROP TABLE dbo.UserName
CREATE TABLE dbo.UserName
(
[ID] [int] IDENTITY(1,1) NOT NULL
, [Name] [nvarchar] (50) NOT NULL
, [Address] [nvarchar] (200) NULL
CONSTRAINT [PK_UserName] PRIMARY KEY CLUSTERED
([ID] ASC)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
SET IDENTITY_INSERT dbo.UserName ON
INSERT INTO dbo.UserName (ID, Name, [Address])
SELECT ID, Name, [Address]
FROM #temp
SET IDENTITY_INSERT dbo.UserName OFF

Answer 3

The easiest way:-
Right click on the table in object explorer and select 'Design'
Select the column for which you want to set identity and go to Column Properties
Under 'Identity Specification' change '(Is Identity)' to 'Yes'
Click Save.... Done :)
Hope This Helps

Answer 4

Here is a solution that is minimally logged.
SELECT
IDENTITY(INT, 1,1) AS ID,
Name, [Address]
INTO dbo.UserName_temp
FROM dbo.UserName;
ALTER TABLE dbo.UserName_temp
ADD CONSTRAINT [PK_UserName] PRIMARY KEY CLUSTERED;
DROP TABLE dbo.UserName;
EXEC sp_rename 'dbo.UserName_temp', 'UserName';
SRC:
http://sqlmag.com/sql-server/appending-identity-column-temporary-table
But the IDENTITY() function can "only in a SELECT statement with an INTO table clause."
http://msdn.microsoft.com/en-us/library/ms189838.aspx