Question

I have a data structure where students and groups have many-to-many relationship. I have three tables

students: id, name

groups: id, name

students_groups: student_id, group_id

How do I select only students who are not in a specific group (e.g. group.id = 1)?

I did some searching and tried using sub query but only get an empty set…

select * from students where not exists (select students.* from students left join students_groups on students_groups.student_id = student.id where students_groups.group_id = 1);

how should I query? thx much in advance!

EDIT
OK, it seems the following two finally works… can anyone EXPLAIN to me why I don’t need to join table for it to work???

select * from students where not exists (select * from students_groups where students_groups.student_id = student.id and student_groups.group_id = 1);

select * from students where id not in (select student_id from students_groups where group_id = 1);

Answer 1

Using a NOT IN should work fine:

SELECT * FROM Students
WHERE Id NOT IN (
    SELECT Student_Id FROM Students_Groups
    WHERE Group_Id = 1)