Question

I would guess this is a semi-common question but I can’t find it in the list of past questions. I have a set of tables for products which need to share a primary key index. Assume something like the following:

product1_table:
    id,
    name,
    category,
    ...other fields

product2_table:
    id,
    name,
    category,
    ...other fields

product_to_category_table:
    product_id,
    category_id

Clearly it would be useful to have a shared index between the two product tables. Note, the idea of keeping them separate is because they have largely different sets of fields beyond the basics, however they share a common categorization.

UPDATE:

A lot of people have suggested table inheritance (or gen-spec). This is an option I’m aware of but given in other database systems I could share a sequence between tables I was hoping MySQL had a similar solution. I shall assume it doesn’t based on the responses. I guess I’ll have to go with table inheritance… Thank you all.

Answer 1

It’s not really common, no. There is no native way to share a primary key. What I might do in your situation is this:

product_table
    id
    name
    category
    general_fields...

product_type1_table:
    id
    product_id
    product_type1_fields...

product_type2_table:
    id
    product_id
    product_type2_fields...

product_to_category_table:
    product_id
    category_id

That is, there is one master product table that has entries for all products and has the fields that generalize between the types, and type-specified tables with foreign keys into the master product table, which have the type-specific data.