Hi Guys, I'm really confused with how the foreign key works. I'm copying a database diagram into mysql for learning purpose and I came across a strange scenario:

Table Screens
================
screenid varchar(12) <PK, FK1> NOT NULL
hearderid varchar(12) <PK, FK2> NOT NULL
bodyid varchar(12) <PK, FK3> NOT NULL
comment varchar(40) NULL
================


So... question. Why is there a primary key with a foreign key and why is the PK and FK together. Also, why do we have multiple PK's.

I'm really confused any clarification would be awesome.

let's take the second question first

there is only one PK, but it is a composite key, consisting of three columns

what that means is that the combinations of the three values are unique, even though a given value in any one of those three columns might occur multiple times

as for the FKs, each of them is a foreign key to its own separate table

Thank you.

In this DB theres going to be about 10 normalized tables with similiar PK/FK relationships. Thing is that I have to MYSQLIMPORT the data first.

So, is it best to set the PK-FK after I import the data?

Do you have a sample schema of how such a PK-FK relationship would look in a create/alter table?

Does this look like a good translation?

Does my create table look right (based on the table from the 1st post)?

if those e id columns in the referenced tables are also VARCHAR(12), then yes

but isn't that a bit unusual? most people use numeric columns

Thanks for the help! Yes it is strange that they are varchar(). I think they did this to protect the DB in case of future changes. Only thing that would make sense to me.