title: sqlite3 selecting all 1:n values from an n:n table
body: <p>I have an sqlite table that relates 2 entities, in the form</p>
  <pre><code>x | y
  1   1
  1   3
  2   2
  2   3
  3   1
  3   2
  3   3
  </code></pre>
  <p>Expected output: 3
  (because x=3 links to y=1,2,3, aka all values of y)</p>
  <p>I need to select all values in x that have a relation to every value in y
  My issue is that when I group by x, then check how many y-values there are for a given group of x's,
  I don't know how many y values there are total because I just grouped my table by x's and can't access the original one to count.</p>