Relation on a multi-valued field in an Access database - database

Question

Does someone know how I can put more than one value in one field to make a relation between two different records?
Google translation (from German):
Using multivalued fields
In most systems, DBMS (database management systems), including earlier
versions of Microsoft Access, you can only store a single value in a
field. In Microsoft Office Access 2007, you can also create fields
that contain multiple values​​, such as a list of categories to which
you have assigned a condition. Multivalued fields are used in specific
situations, such as when you use Office Access 2007 to work saved in a
Windows SharePoint Services 3.0 list that contains a field of one of
the field types with multiple values ​​that are available in Windows
data SharePoint Services.
This topic describes how to create and use multivalued fields in
Office Access 2007 and Windows SharePoint Services, how to create
multivalued fields and used, and how to use multivalued fields in a
query.

Answer 1

You can use multi-value Lookup fields in JOIN conditions (via their .Value property), but be aware that if there is such a field on both sides of the join then it will produce a match when any item matches on the joined fields, not when all items match. This may or may not be desirable, depending on the situation.
Case 1: Students with allergies
A school administrator needs to keep track of students with allergies and provide them with a list of meals that they should avoid when eating at the school cafeteria.
[Students]
ID Student Allergies
-- ------- ---------
1 Alice Eggs, Soy
2 Bradley Peanuts
3 Carol
4 Dennis Soy
[Meals]
ID Meal Allergens
-- ------------- ---------
1 Thai stir-fry Peanuts
2 Tofu omlette Eggs, Soy
3 Waffles Eggs
The query
SELECT Students.Student, Students.Allergies, Meals.Meal, Meals.Allergens
FROM Students INNER JOIN Meals ON Students.Allergies.Value = Meals.Allergens.Value;
returns
Student Allergies Meal Allergens
------- --------- ------------- ---------
Alice Eggs, Soy Tofu omlette Eggs, Soy
Alice Eggs, Soy Waffles Eggs
Bradley Peanuts Thai stir-fry Peanuts
Dennis Soy Tofu omlette Eggs, Soy
This is appropriate, since Alice should avoid meals that contain any ingredients to which she is allergic.
Case 2: Hotel requirements
[Travellers]
ID Traveller Requirements
-- --------- -------------------------
1 Gord free WiFi, in-room coffee
[Hotels]
ID Hotel Amenities
-- ------------ ----------------------------
1 Budget Motel free WiFi, in-room coffee
2 Fancy Hotel in-room coffee, room service
The query
SELECT Travellers.Traveller, Travellers.Requirements, Hotels.Hotel, Hotels.Amenities
FROM Hotels INNER JOIN Travellers ON Hotels.Amenities.Value = Travellers.Requirements.Value;
returns
Traveller Requirements Hotel Amenities
--------- ------------------------- ------------ ----------------------------
Gord free WiFi, in-room coffee Budget Motel free WiFi, in-room coffee
Gord free WiFi, in-room coffee Fancy Hotel in-room coffee, room service
The query returns both properties because they both offer in-room coffee. However, Fancy Hotel does not offer free WiFi, so I would prefer not to stay there. In this case the default join behaviour is not desirable (to me).