Referencing the primary table in a sub-query

Question

I have tables with some relations:

create table Students
(
    [id] uniqueidentifier not null,
    primary key (id),
    [group] uniqueidentifier FOREIGN KEY REFERENCES [Groups]([id]) not null,
    [name] nvarchar(20),
    [surname] nvarchar(20)
)

create table Books
(
    [id] uniqueidentifier not null,
    primary key (id),
    [name] nvarchar(100) not null,
    [pages] int not null,
    [author] uniqueidentifier FOREIGN KEY REFERENCES [Authors]([id])
)

create table StudentsCards
(
    [id] uniqueidentifier not null,
    primary key (id),
    [student] uniqueidentifier FOREIGN KEY REFERENCES [Students]([id])
)

create table RelationsBooksToStudentsCards
(
    [book] uniqueidentifier FOREIGN KEY REFERENCES [Books]([id]) not null,
    [students_card] uniqueidentifier FOREIGN KEY REFERENCES [StudentsCards]([id]) not null
)

And I have query which trying to get sum of pages by students:

SELECT 
    [id] AS student_id, [name], [surname], 
    (SELECT SUM(b.pages)
     FROM Students AS s
     INNER JOIN RelationsBooksToStudentsCards AS r ON (SELECT [id] FRM StudentsCards WHERE student = s.id) = r.students_card
     INNER JOIN Books AS b ON r.book = b.id
     WHERE s.id LIKE student_id) 
FROM
    Students

Question: what do I need to do to use student_id in the query? Because now I got an exception:

Invalid column name 'student_id'

Answer 1

Ah, it was easy:

select [id], [name], [surname], (SELECT sum(b.pages)
FROM Students as s
inner JOIN RelationsBooksToStudentsCards as r
    ON (select [id] from StudentsCards where student = s.id) = r.students_card
inner JOIN Books as b
    ON r.book = b.id
where s.id like myAlias.id) from Students as myAlias