sqlite3 selecting all 1:n values from an n:n table

Question

I have an sqlite table that relates 2 entities, in the form

x | y
1   1
1   3
2   2
2   3
3   1
3   2
3   3

Expected output: 3 (because x=3 links to y=1,2,3, aka all values of y)

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.