SQL Joins through Virtual Foreign key


#1

How do we create relationship b/n two tables with more than one key ?

Table A has Column AA, Column AB, Column AC, Column AD out of which Column AA and Column AB are Primary Composite key defined in the database.
Table B has Column BA, Column BB, Column BC, Column BD out of which Column BB, Column BC are Primary composite key defined in the database.

I want to join this tables based on Column AA = Column BA and Column AC = Column BB. Please let me know how this can be achieved through Virtual Foreign key concept.

I am using MySQL as my back end database.