First_Value, Last_Value and Lead function in Sql Server 2012

create table #temp1

(

userid int,

username varchar(50)

)

insert into #temp1

select 12,'siba'

union all select 13,'anurag'

union all select 13,'abhishek'

union all select 14,'ravi'

union all select 14,'anurag'

union all select 15,'siba'

union all select 19,'siba'

select 12,'tom'

select userid,username,first_value(userid) over(order by userid desc) as firstvalue,last_value(userid) over(order by userid desc) as lastvalue

 from #temp1

-------------------------------------------------------------------------

select userid,username,first_value(userid) over(order by userid desc) as firstvalue,last_value(userid)  over(order by userid desc) as lastvalue,

lead(userid) over(order by userid asc) as leaduserid

from #temp1

-->Last_value is actually the row currently which we are looking at and Lead is the subsequent row value