In case if user wants identity also in varchar column for the above scenario..
drop table testtable2
go
CREATE TABLE TestTable2 (
srlNo int NOT NULL IDENTITY(1, 1),
Id varchar(100),
Name varchar(50) NULL,
Addres varchar(100)
) ON [PRIMARY]
go
insert into TestTable2 values('test1','sant','test')
go
CREATE TABLE TempTable2 (
Identifier int NOT NULL IDENTITY(1, 1),
Id as 'test'+cast(Identifier as varchar(100)),
Name varchar(50) NULL,
Addres varchar(100)
) ON [PRIMARY]
go
SET IDENTITY_INSERT TempTable2 ON
go
IF EXISTS ( SELECT * FROM TestTable2 )
INSERT INTO TempTable2 (Identifier, Name,Addres )
SELECT srlNo,Name, Addres FROM TestTable2
TABLOCKX
go
SET IDENTITY_INSERT TempTable2 OFF
go
DROP TABLE TestTable2
go
Exec sp_rename 'TempTable2', 'TestTable2'
select * from testtable2