How can delete duplicate rows from table except one row?

This problem can be solved by many ways. But I have two simple method :-
1) using  simple sub query Method
2) using Rowcount

1) delete
   top (select count(*)-1 from TableName where Condition )
   from
 TableName where Condition .
Note :- Both condition should be same for apropriate result.

2) RowCount is very usefull keyword in sqlserver. By this way we can fix , how many row will be affected .
suppose in a table we have n number of rows , we want to display only 1 row , just write down
     set rowcount 1
after that any DML or DDL command effects only one row of  table.
and ,
    set rowcount 0 , for all rows from table
For the above problem , at first get number of similar rows from table using " select count(*) from TABLENAME  where Condtion " (suppose get n rows , where n is integer)
Then
set rowcount  n-1
delete  from  TABLENAME  where  Condition
set rowcount 0

What is a GUID and How to create a GUID in C# ?

GUID --->   Globally unique identifier   -  128-bit integer
GUID  can be used to uniquely identify something
This method can be in system name space . GUID method System.Guid.NewGuid() initializes a new instance of the GUID class.
Syntax -   System.Guid.NewGuid();
Each time get a new number.

Difference between cast() and convert() in sql server 2005.

Both function are used in Sql server for explicit conversion of data from one data type to another data type. But using convert() function , data will convert in formated manner , not in cast() function.
For Example:-
cast()
cast(data as datatype)
select cast(getdate() as varchar(100))
output -- Nov 29 2010  5:39PM

convert()
convert(datatype,data,formate)
select  convert(varchar,getdate(),105)
output -- 29-11-2010

what is optimistic and premistic locking in Database

Optimistic locking assumes that no one would read or change the data while changes are being by a bean
Pessimistic locking would rather lock down the data so that no one can access it

or


In optimistic locking the row will not be locked until the actual update is performed. In order to prevent the lost update issue a version number column will be used. In pessimistic locking the row will be locked at the time when the data is selected from the database. This will prevent other users who want to update the same record. This should not prevent the readers but this behaviour varies from database to database.

What are Magic tables in SQL SERVER

There are two magic tables named inserted and deleted.

On Insertion :
whenever an insert takes place, the data goes into inserted
table before the commit of the transaction.

On Deletion :
Whenever a row gets deleted from a table, data goes into
deleted table.

On Update :
Since an update statement is a combination of delete and
insert so in case of update data goes in both, inserted and
deleted tables.

some usefull code of C#

click on this link for some usefull C# code

http://www.fincher.org/tips/Languages/csharp.shtml

What does NULL mean?

The value NULL is a very tricky subject in the database world, so don't be surprised if several applicants trip up on this question.
The value NULL means UNKNOWN; it does not mean '' (empty string). Assuming ANSI_NULLS are on in your SQL Server database, which they are by default, any comparison to the value NULL will yield the value NULL. You cannot compare any value with an UNKNOWN value and logically expect to get an answer. You must use the IS NULL operator instead.