Question

If I had a PERMISSIONS table that looked like this:

PERSON         PERMISSION
------         ----------
Bob            red
John           red
John           blue
Mary           red
Mary           blue
Mary           yellow

and a THINGS table that looks like this:

THING          PERMISSION
-----          ----------
apple          red
eggplant       red
eggplant       blue

I’m trying to come up with a pure SQL query that would let me find out what PERSONs have access to what THINGs. Basically, I want a query that would look something like:

SELECT person
  FROM ... vague handwaving here ...
 WHERE thing = 'eggplant'

and have it return “John” and “Mary”. The key point being the number of permissions necessary for access to the thing is arbitrary.

I feel like this should be obvious, but I just can’t come up with an elegant solution. Oracle compatible solutions preferred.

Edit:

Solutions from Kosta and JBrooks work well. Below is a modified version of Kosta’s solution that only hits the indexes twice, as opposed to 3x for Kosta’s and 4x for JBrooks’s (though I agree with JBrooks that this is probably unnecessary optimization).

SELECT p.person, num_permission, COUNT(p.person)
FROM permissions p
INNER JOIN (
    SELECT permission,
           COUNT(1) OVER (PARTITION BY thing) AS num_permission
      FROM things
     WHERE thing = 'eggplant'
  ) t ON t.permission = p.permission 
GROUP BY p.person, num_permission
HAVING COUNT(p.person) = num_permission

Answer 1

select person
from permissions 
where permission in (select permission from things where thing='eggplant')
group by person
having count(person) = (select count(permission)  from things where thing='eggplant')