Foreign Keys

[RustyRick]

Foreign Keys to NOT yet have asylum in my head yet?

I know what FK are for - linking tables. I know where they sit in tables. I have watched countless YouTube videos and in my 73 year old mind nobody has clearly defined them?

I see example like "CONTACT Number", and "ContactNumber" being used and called Foreign Keys. Spelt different on 2 different tables. I understand they both must be the same data type.

BUT - I don't understand what exactly determines that 2 field descriptions become Foreign Keys?

[CJ_London]

it is defined in relationships. Many of the templates and examples you will find try to 'keep it simple' rather than being 'correct'. PK's are unique to a table, you will never find a duplicate. FK's can have duplicates because they relate back to one PK. The field names themselves are irrelevant but my own preference is to name fields with a PK or FK suffix to identify which end of a relationship a field is. Using an invoice as an example - you have one invoice header record (has a PK), but many invoice lines that relate back to that one invoice header. So the invoice line record will have a PK to uniquely identify the individual line but also a FK field to link back to the invoice header.

With regards field names, you should think of them in the context of the whole application, not just the table. So 'ID' or 'Description' may be sufficient within the context of the table, but not the application - ID of what? description of what? Better to use a name like 'customerFK', 'customerPK', 'ProductDesc', etc