IS there a possibility to get the "same" attribute into one column from different tables?

Question

So I have two the two tables with a primary key month_cd:

Table A:

month_cd	stuff	stuff2
First	1	null
Second	2	null
Third	null	2

Table B:

month_cd	stuff	stuff2
First	null	2
Third	3	null
Fourth	4	3

I need them to look like this in the third table C.

Table C:

month_cd	stuff	stuff2
First	1	2
Second	2	null
Third	3	2
Fourth	4	3

I tried doing full outer join with coalesce(A.month_cd, B.month_cd, C.month_cd), but somewhy it gives me doubles like

Table C:

month_cd	stuff	stuff2
First	1	null
First	null	2
Second	2	null
Third	3	null
Third	null	2
Fourth	4	3