Comparing Database and Inserting values

Question

Hello Every one,

I am working on databases and I need some advice from you guys.

I have 2 databases with many rows and columns and these db's contain addresses of customers.

Lets name the databases a A,B.

Now the problem is I have to search the addresses of B in A using a primary key lets say email.

If the address exist then its ok.

Else we have to insert the address in to the other database.

Please tell me how can we do this and which language we can use to do this??

Thank you very much for your time to read my question