Subject Primary keys - was Copy records
Author Planles
> A table can never have two primary keys. Only one. Any unique
> column can
> be the primary key; or a combination of columns where every instance of
> the combination is unique.

I'm a little bit confused now, so I'm asking for a little more explanation.
My example:

M_id, M_desc, M_desc2,...

MC_id, MC_key, MC_qty,...

Each record in Table1 can have multiply records in Table2.

Now I had M_id in Table1 as primary key, and MC_id and MC_key from Table2 as
primary key. MC_id is equal to M_id, and MC_id and MC_key is a unique pair.

Could you explain me, how should I proper do this relationship.