SQL field with multiple id's of other table

Question

Could someone give me an idea how to create this database structure. Here is an example:

Table \"countries\":
id, countryname
1, \"US\"
2, \"DE\"
3, \"FR\"
4         


        

Answer 1

What you're talking about is normalisation. You have a many-to-many structure, so you should create another table to link the two. You should never (ok, pretty much never) use delimited strings to store a list of values in a relational database.

Here's an example of the setup:

product_countries table

productid | countryid
----------+-----------
1         | 1
1         | 2
1         | 4
2         | 2
2         | 3
2         | 4

You can use a foreign key to each other table, then make them both into a composite primary key.

You can then get a list of supported products for a country ID like this:

SELECT * FROM products, product_countries
WHERE products.id = product_countries.productid
AND product_countries.countryid = $cid