500*500 is only a quarter million row Cross Join and would probably take less than a quarter second to materialize and just a second or two to insert into an indexed table.

For the million row thing, you definitely have to be careful because 1*10^6 squared is 1*10^12 or a Trillion rows. Some of this could be mitigated by using a "Triangular" join, which would produce a bit less than half that of a full up Cross Join but 500 Billion rows is still nothing to sneeze at either duration wise or storage wise.

My recommendation would be to NOT turn this "Matrix" into a table.