Showing non matching records between two tables based off shared key.
I have two tables Table A and Table B. Basically what I want to do is find the non matching records between the two tables based off a key variable. For instance if table A has 2 records and table b has 4 records but 2 of the records match with table a, I want to know the 2 that aren't matching. I later want to add the two non matching records in table b to table a. Any help would be much appreciated.