This is my first question and first day in Linq so bit difficult day for me to understand. I want to fetch some records from database

i.e.

select * from tblDepartment 
where department_id in 
(
   select department_id from tblMap 
   where Guest_Id = @GuestId
)

I have taken two DataTable. i.e. tblDepartment, tblMap

Now I want to fetch this result and want to store it in third DataTable.

How can I do this.

I have been able to construct this query up till now after googling.

var query = from myrow in _dtDepartment.AsEnumerable()
            where myrow.Field<int>("Department_Id") == _departmentId
            select myrow;

Please provide me some link for learning Linq mainly for DataTables and DataSets.

EDIT:

I have got a very similar example here but i m still not able to understand how it is working. Please put some torch on it.