Big performance bug if true

https://mariadb.com/docs/server/reference/data-types/serial
says serial is an alias for: `BIGINT UNSIGNED NOT NULL AUTO_INCREMENT UNIQUE`

But it also acknowledges that `This shorthand data type is often used to define primary keys.`

Which means, most people who use `serial` do it like `id SERIAL PRIMARY KEY`

Which means, *Two* separate indexes get created on the same key, most of cases, some sort of id.

Which in turn, eats up space and performance unnecessarily.

I think a good solution would be to remove `unique` off `serial` or replacing it with `primary key` as default. i don't know.