Combining Two Tables

I have a query that joins two tables with a full join therefore it should select all data from both tables.

This works fine if I don't use any criteria.

However I want to be able to select a month from each table (the month may be different) for example month 7 in tableA and month 5 in tableB

If I use where tableA = 7 and tableB = 5

This now only works if there is matching data (based on a common field) in both tables.

I want to be able to select all the month 7 data from table A and all the month 5 data from table B and add them together in a query.

Thanks for your help