Many-to-many sql select query containing multiple values, all values are taken into account

There is the following database structure:

How do I write a query that returns only those Questions that have both CSS and JS tags?

Answer

You can use aggregation and having:

select tq.question_id
from tagsquestions tq join
     tags t
     on tq.tag_id = t.id
where t.name in ('JS', 'CSS')
group by tq.question_id
having count(*) = 2;

This assumes that the tags assigned to a single question are distinct. That seems like a reasonable assumption.