You should not have more than one primary key in your table. You might have a composite primary key - which is a single primary key consisting of more than one field.
This wiki uses an sql read on such a composite key (see Another use case…) if you would be interested.
I think you misunderstood him There is no relational database I am aware of that supports tables with more than one primary key. However, primary keys covering more than one field (a.k.a. composite primary keys) are well supported.
Well Nightmove, if you add secondary indexes and make them each unique, then I guess you could "treat" them like many primary keys. The wiki I mentioned does exactly that in the junction table.
I’m actually going to sit with this same problem soon because I need to create a table where some users want to use a numeric key; others want to use an alpha key; and others an auto-increment key. So I will have to include all three and treat them as different primary keys. Wish me luck.
Let us know if you find an answer to your problem.