Fetch Data Using While Loop From A Table With Identity Column

A simple way to fetch data one by one using while loop if table has a identity or primary key.

Assume that I am using the below table and need to fetch one by one all rows and do some operation on each row data. 
Table structure 
  1. CREATE TABLE [dbo].[User_Login](  
  2. [userid] [int] IDENTITY(1,1) NOT NULL,  
  3. [Username] [varchar](100) NULL,  
  4. [User_Pass] [varchar](100) NULL,  
  5. [F_Name] [varchar](20) NULL,  
  6. [L_Name] [varchar](20) NULL,  
  7. [Address1] [varchar](200) NULL,  
  8. [mobile] [varchar](20) NULL,  
  9. [City] [varchar](20) NULL  
  10. )  
We can use a while loop, get the column data and do some operations.  
  1. declare @cnt int  
  2. declare @UnitCount int  
  3. set @cnt=1  
  4. set @UnitCount=(select count(*) from User_Login)  
  5. while @cnt<@UnitCount  
  6. begin  
  7. select top(1)* from User_Login where userid not in(select top(@cnt-1) userid from User_Login) order by userid  
  8. --Do your operation like fetch data into variables and update it into another table etc..  
  9. set @cnt=@cnt+1  
  10. end