Question:

What should I do when I face a challenge of using a composite primary key.

The situation is that I have a table named dish.

It has certain parameters/fields which are all dependent on cell id, but one area of the application has to deal with the freq a dish can accept or emit.

Now the dish will use 2 major freq , 1800 MHz and 900 MHz.

What should I do? I created another table with the following structure: 

Dish id

Tilt

Freq.

Tilting of the dish can be for both the frequencies. The data will be as follows:

Dish1     20     900

Dish1     23     1800

In this case the normalization and database design is working fine but I cannot make Dish1 the primary key.

Can I make dishid and freq both composite as the primary key for the table?

Kindly suggest something so I can get out of this dilemma.

Should I use a sequence? 

Thanks a lot for the reply.

This question posed on 17 November 2005

Answer:

You should use a composite key with both the dishid and freq columns (assuming a dish cannot have more than one frequency)