I am setting up something of a lookup table to track what specials (from another table) appear every day on a restaurant's daily menu...

the table I have created is as follows:

mysql> describe days;
| Field     | Type       | Null | Key | Default    | Extra |
| specialID | int(11)    |      |     | 0          |       |
| date      | date       |      |     | 0000-00-00 |       |
| courseID  | tinyint(4) |      |     | 0          |       |
3 rows in set (0.00 sec)
Apart from the specialD field, which specifies which special we're talking about, and the date field which is self explanatory, I also need to specify wether the special is for lunch or dinner that day (in some cases it might be both).

I guess the primary key, as I imagine it, should be a multi-column primary key, so i can pull the specials for each day's lunch and dinner menus and print them out. What columns should the primary key span though? Can I specify more than two columns for a primary key, and must they be numeric?