title: Return student_ids where at least one of each category
body: <p>Say we have three tables students, assignments, and subjects. I want to return all student_ids where that student has completed at least one assignment in each subject that a student named first_name = 'place' and last_name = 'holder' has.</p>
  
  <p>Student table:</p>
  
  <pre><code>Student_id | first_name | last_name
  ------------------------------------
       1     |   place    | holder
       2     |            |           
       3     |            |
  </code></pre>
  
  <p>Subjects:</p>
  
  <pre><code>subject_id | name
  -----------------
       1     | Math
       2     | English
       3     | Science
  </code></pre>
  
  <p>Assignments:</p>
  
  <pre><code>student_id | subject_id
  -----------------------
       1     |    1
       1     |    2
       1     |    3
       2     |    1
       2     |    2
       2     |    3
       3     |    1
       3     |    2
  </code></pre>
  
  <p>So, in this case I would want my query results to be:</p>
  
  <pre><code>student_id
  ----------
       1
       2
  </code></pre>
  
  <p>I've tried a number of different methods like using set operations and stuff like that but none of them seem to get exactly the right results. I keep getting all the students who have completed at least one assignment in ANY subject that student 'place holder' has completed an assignment in.</p>