No trigger needed!!

Just use an INSERT command. The thing you need to take care of is that the value of "users_id" you enter in the [travel_request] table must allready exists in table [users]. The code below give you two possible solutions. The first will insert all values hard-coded. The second will insert the values and searches the "users_id" that belongs to the given "username".

-- insert values hard-coded

insert into travel_request values(1, 3, 200, 'me')

-- insert values and search the "users_id" from the [users] table

insert into travel_request

select 2, users_id, 500, 'me'

from users

where username = 'Ram'

select * from travel_request