The join will happen automatically when the field name is the same. You can't change that behavior. You can rename the fields so they don't link up.
A quick way to do this is the QUALIFY script statement.
That will preprend the table name to each field name giving you unique field names for each table. You follow the above QUALIFY with an UNQUALIFY to name the fields that you do want to link.
UNQUALIFY CustomerID, ProductIID;
SQL SELECT * FROM Orders;
SQL SELECT * FROM Customers;
SQL SELECT * FROM Products;