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I am just trying to create a simple booking system for a restaurant. I have 5 tables at the moment.

Member ---> Reservation <--- Exclusive Night

Menu ---> Dish

Above shows their relationship with each other. So a customer can make many reservations and many reservations are for one exclusive night.

However i have those other two tables and the bottom Menu and dish, with one menu having many dishes.

Although members and non members can view menus i am not sure how they could be joined by a foreign key, or joined at all.

So my question is, is it wrong/discouraged to have two tables like that which are not linked to the rest of the database?

Thanks for your help.

user667430
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2 Answers2

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Linking data with associations means to constraint data to have values in accord with association.

If you have to represent an associaion between a member and a menu (if you can express it with application context specific words and need to represent it for the purposes of your application logic), so you will design this association and then reduce this association with adding a column to a table (e.g the foreign key for the members in the menu table) and add a constranint to ensure that data in the FK conforms to data in the PK and if you want it you will add REFERENTIAL INTEGRITY.

It's your choice, you don't have to.

In database design you should ask yourself firstly if you need to.

Andrea Colleoni
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It's up you. They are called constraints because you are limiting the possible inputs.

So for instance if

Menus was MenuId, MenuName,DishId and Dishes was DishId, DishName, it's perfect reasonal to say that all dishes on a menu must exist in the dishes table, so you'd put a Foreignkey constraint on menus.

After that things like joining Menus to dishes

To print one out with Egg fried rice instead of 42

Find all the menus which have the cook's special roof rabit on a bed of spinach on.

All dishes that never appear on a menu.

are all things you might want, but what you are sating you don't is a dish on a menu 'you' know nothing about.

Relationships is the mechanism, contraints is the reason.

Tony Hopkinson
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