Question

So I have a database with a few tables.

The first table contains the user ID, first name and last name.

The second table contains the user ID, interest ID, and interest rating.

There is another table that has all of the interest ID’s.

For every interest ID (even when new ones are added), I need to make sure that each user has an entry for that interest ID (even if its blank, or has defaults).

Will foreign keys help with this scenario? or will I need to use PHP to update each and every record when I add a new key?

Answer 1

For every interest ID (even when new
ones are added), I need to make sure
that each user has an entry for that
interest ID (even if its blank, or has
defaults).

It sounds like you need an OUTER JOIN (either LEFT or RIGHT) in one of your queries instead.

For example, if you wanted to get the level of interest a particular person has for each interest:

Assuming your tables look like this:
users:
user_id PK
user

user_interests:
user_id PK FK
interest_id PK FK
interest_level

interests:
interest_id PK
interest

SELECT i.interest, ui.interest_level
FROM interests i
INNER JOIN user_interests ui USING (interest_id)
LEFT JOIN users u USING (user_id)
WHERE user_id = ?

? is a placeholder.

Note that ui.interest_level will be null for interests with no data.