sql Trigger

Question

I have Some Leave_Details :- 

userid   Name       UserName         startdate enddate         leavetype LeaveRequestID ApproveUnapprove

409 Ashok     ashok        2012-09-01 2012-09-01 Sick    933   Null

493 Ravi            ravi       2012-09-17 2012-09-18 Personal    922   Null

400 Ro         rohan        2012-09-19 2012-09-21 Planned    923 Null

524 Ravi     ravi        2012-09-20 2012-09-20 Planned    927 Null

409 Ashok   ashok        2012-09-28 2012-09-28 Persona     937 Null

How to Approve in Automtically in sql trigger please give me a examples