Relationship between Table A and B without using Primary Key on table A

Hi

I have a table called Leads. The primary key on this table is the "Record ID#" field. Leads eventually open accounts and the Lead records "Account Number" field gets updated with the account number of the account they opened.

Im trying to build a relationship between the Leads table and Sales table. the Sales table contains the account number that places orders with us, the relationship needs to be between the Account Number field on the Leads table and the Account number field on the Sales Table, neither of these account number fields act as a primary key.

Is there a way to do this? Essentually i want to be able to have fields on the Lead table showing the number of orders placed and total sales number taken from the sales table.

Thanks