SQL query to return an exact list of subquery

Question

So I am given this question:

Consider the following tables where keys are bolded: Professor(profid, profname, department) Student(studid, studname, major), and Advise(profid, studid).

Return the names of the students who have exactly the same advisors as student whose id is '123456789'.

The query that I came up with doesn't return the exact same advisors, but rather the advisors that are common between student 123456789 and other students. An example is if student 123456789 has advisors 1 and 2, and student 5 only has advisor 1, my current query will return student 5, which is incorrect. The query is only supposed to return students that have both advisors 1 and 2. Here is my query so far:

SELECT studname
FROM Student
WHERE studid IN 
(
    SELECT DISTINCT studid
    FROM Advise
    WHERE profid IN
    (
        SELECT profid
        FROM Advise
        WHERE studid = '123456789'
    )
);

How can I get this query to return the exact list of students that advise student 123456789?

Answer 1

I test it run right. You can try:

SELECT a.studid, b.studname
FROM (
    SELECT studid, COUNT(studid) AS numstud
    FROM Advise 
    WHERE 
        profid IN (
            SELECT profid FROM Advise WHERE studid = 123456789
        ) AND 
        studid NOT IN (
            SELECT studid FROM Advise WHERE profid NOT IN (
                SELECT profid FROM Advise WHERE studid = 123456789
            )
        )
    GROUP BY studid
    HAVING numstud = (SELECT COUNT(*) FROM Advise WHERE studid = 123456789)
) AS a LEFT JOIN Student AS b ON (a.studid = b.studid)