An SQL query to get the exact matching results - mysql

Question

In my MySQL database, I have three tables students, classes, courses.
One class has many students.
One class has many courses.
The courses table has one boolean field active, and a string field name.
So overall relationship is (sorry I am not sure how to better illustrate the relationship if it is not clear) :
students (many_to_one) classes (one_to_many) courses
I have a function in Ruby that accepts an array of strings argument for the course names:
def get_student_names_whose_courses_are(active_course_names)
# Run a raw SQL query for the result
end
I would like to write a raw SQL query to get the names of students whose courses (via class) matches exactly the passed in argument course names and are active.
For example, if active_course_names holds values ['foo','bar']. Student-A has active courses 'foo','bar','etc', student-B has active courses 'foo' and 'bar'. The raw quesry should only return student-B, even though student-A also has the two courses active, the point is an exact matching.
What I tried is this:
select stu.name
from students stu
inner join classes clz ON clz.id = stu.class_id
inner join courses cour ON cour.class_id = clz.id AND cour.name in (#{active_course_names,join("','")})
where cour.active = true;
But with this, it returns both student-A and student-B for the example above. How to make the query so that it returns students that have exactly the active courses?
My demo exapmle here

Answer 1

I hope the following answer would be of help to your problem.
If you assign a rank in the same courses (for instance 'FOO'), then you can keep the courses which are repeated in the classes (rank>1) and apply your list of courses. After creating that, you can perform the join to bring the students' information that you need.
SELECT Temp.name,stud.id,stud.name,stud.class_id
FROM (
/*Create a view with the courses which are present with another classroom*/
SELECT T.id, T.name, T.active,T.class_id
FROM (
/*Create a view with only the active courses and their rank*/
SELECT id,name,active,class_id,
#course_rank := IF(#current_course = name,
#course_rank + 1, 1) AS course_rank,
#current_course := name
FROM courses,(select #current_course :=0,#course_rank :=0) r
WHERE active = 1
ORDER BY name, class_id ASC)T
/*Create a filter to bring only the classrooms with the same courses and the selected courses*/
WHERE T.course_rank>1 AND T.name IN ('foo','bar'))Temp
JOIN students stud
ON Temp.class_id=stud.class_id

Answer 2

You can use group_concat like this :
SELECT
stu.name,
GROUP_CONCAT(cour.name ORDER BY cour.name ASC) AS courses
FROM students stu
inner join classes clz ON clz.id = stu.class_id
inner join courses cour ON cour.class_id = clz.id
where
cour.active = true
GROUP BY stu.name
HAVING GROUP_CONCAT(cour.name ORDER BY cour.name ASC) = 'bar,foo'
DEMO IS HERE

Answer 3

Try this:
select distinct student from (
select stu.name student, cour.name course, count(cour.name )
from students stu
inner join classes clz ON clz.id = stu.class_id
inner join courses cour ON cour.class_id = clz.id
where cour.active = true
and cour.name in ('foo','bar')
group by stu.name , cour.name
having count(course) =2) A;
Here is the DEMO
In this DEMO only stu-A needs to be selected.
Number 2 marks that student only has this two courses active and not 3 of them. Hope this is it...