As pointed out by @ErwinSmout the first example is incorrect. If I understand correctly C doesn't depend on neither A nor B so given r like:
r1 = (1,4,6)
r2 = (1,4,7)
A | B | C
---|---|---
1 | 4 | 6
1 | 4 | 7
1 | 4 | 6
1 | 4 | 7
We will get doubled rows after joining it back together. Also
multiple A can have the same B so then you would end up with incorrect values.
r1 = (1,4,6)
r2 = (2,4,7)
A | B | C
---|---|---
1 | 4 | 6
1 | 4 | 7
2 | 4 | 6
2 | 4 | 7