There is a table with common companies and it is necessary to create a table that shows that one company from the common table can supply several types of goods to another company from the same table. Implemented it by creating an indexed supplier_recipient table, in which there are 3 attributes with the type of product, sellers, recipient. ( key_product_type , key_supplier , key_supplier ). Created a subordinate form for implementing many-to-many communication. 
And everything seems to be fine, but in the list boxes we need to refer to the general_data table, which is not explicitly defined in the supplier_recipient table, but through the common table: 
resulting in an error: 
Question: How to create working combo boxes with no explicit link?
The database is here .
