Performance for using 2 where clauses in LINQ

Question

In LINQ-to-Entities you can query entities by doing:

var students = SchoolContext.Students.Where(s => s.Name == "Foo" && s.Id == 1);

I know that behind the scenes it will be translated to SQL to something similar to:

SELECT *
FROM Students
WHERE Name = 'Foo' AND Id = 1

However is there a difference (with respect to performance) if I write:

var students = 
    SchoolContext.Students
        .Where(s => s.Name == "Foo")
        .Where(s => s.Id == 1);

Will it be translated to the same SQL query? From my understanding .Where() will return IEnumerable<T> so the second .Where() will filter the entities in-memory instead of translating the IQueryable<T> to SQL, is that correct?

Answer 1

The first .Where() clause will still return an IQueryable<T>. As long as you are operating on an IQueryable<T> it will continue building up the SQL query and execute it when the collection needs to be brought into memory (eg: as @anaximander stated when used in a foreach loop or ToList() operation.

Therefore:

SchoolContext.Students.Where(s => s.Name == "Foo").Where(s => s.Id == 1);

Still translates into:

SELECT *
FROM Students
WHERE Name = 'Foo' AND Id = 1

Whilst the below 2 statements will translate into the same query:

SchoolContext.Students.Where(s => s.Name == "Foo").Where(s => s.Id == 1);
SchoolContext.Students.Where(s => s.Name == "Foo" && s.Id == 1);

Answer 2

First Where returns IQueryable<T> so there will be no performance difference.