Question

@Parameter = (some_value)
select * from C1
where C1.number = 
(select number from C2
where id = @Parameter)

pointers to good resources for learn the concepts of linq to entities will also be helpful.
Thanks

Answer 1

You can use the following format:

var p = parameter;

from c in C1
where C.number == ( from x in C2
                   where x.id == p
                   select x).FirstOrDefault()
select c;

Here is the official MSDN documentation with examples for Linq To Entities.