UNION or JOIN?

[Augusto César]

Hey all! Long time, no see!

I am having a big problem with two tables and I cant get the result I want.

The tables are:
Table A
A1 - A2 - A3
1 - 9 - 2
1 - 10 - 2
2 - 9 - 3
2 - 10 - 3
3 - 9 - 2
3 - 10 - 2

Table B
B1 - B2 - B3
1 - 8 - 1
2 - 9 - 1
3 - 10 - 0
4 - 9 - 1

What I want is:
Table results:
R1 - R2 - R3
1 - 8 - 1
1 - 9 - 2
1 - 10 - 2
2 - 9 - 3
2 - 10 - 3
3 - 9 - 2
3 - 10 - 0
4 - 9 - 1

Explaing the R table:
R2 - A2 || B2
R3 - if(B2 && A2) B3 * A3; else B3 or A3;

I tried to use JOIN and it gave some results, the UNION gave me the results that JOIN missed.

So, the problem is, I do not know how to get those results, could anyone help me please?

See ya!

Augusto