Primary key - assignment 2 ?

Can anyone please explain to me what the underline and double underline means in the tables for assignment 2.

eg. CHARGES (Patient_Num,Item_Code,Charge)
----------- ---------
---------

1. Are these 2 keys or just one primary key made up of 2 fields?
2. Or maybe a primary and foreign key?

Thanks

Hmm, I was following the diagram on pg21 of the tut and made all the boldface names primary keys

It is confusing because in Access table design the only way to show 2 x key icons as they show in the diagram is to make a composite key of two or more fields.

I emailed the lecturers almost 2 months ago and still no answer about this.

If you analyze it carefully you'll come to the conclusion that both fields represent a combined primary key.

The reason for this is:
- both fields are in fact foreign keys
- there is no primary key defined

I agree with your conclusion but I still wonder why they have Patient_Num as a single underline and Item_Code as double. Somehow I think they mean different things and I just can't remember why?

It probably does not matter if they are foreign keys or primary keys as a foreign key is a primary key in another table anyway.

How about the other database experts on this forum. Any more ideas?

I did this course last year, and, if I remember correctly, a single underline = Primary key, double underline = Foreign key.

If you look at the definition and the examples, you'll see that Patient_Num is the primary key for both Charges and Patient tables. Item_Code is your "link" to the Item table.

Somewhere in our notes (or the text book), there was definately an explaination about the single and double underline and about combined Primary keys. I don't have that with me, so, you'll have to go and search for those definitions yourself.

Good luck.

Reanie

Single underline indicates the primary key.
Double underline indicates the foreign key.