以正确的方式使用PRIMARY KEYS（处理语言环境）

Question

I have a table called countries that has the structure: ID, LOCALES_ID, NAME

I want to handle multiple locales with this table, so I need that for different LOCALES_ID, the ID is the same. So, if I insert:

INSERT INTO countries (locales_id, name)
VALUES
('1', 'Lorem'),
('2', 'Ipsum');

The final result I want on the database is:

ID | LOCALES_ID | NAME
1  | 1          | Lorem
1  | 2          | Ipsum

But with the INSERT I tried I got the next result:

ID | LOCALES_ID | NAME
1  | 1          | Real insert
2  | 2          | Real insert #2

My countries table has a PRIMAY index on the columns ID and LOCALES_ID and I supposed that this was all what I need for when I insert different locales I get the same ID.

How I can solve this problem?

Thank you in advance,

Answer 1

What you're trying to implement here is a one-to-many relationship, ie each Country can have multiple Locales. This cannot be achieved with a single table, as you would find yourself with the same Country appearing multiple times. What you should do is split the data in two tables. You can find an example below.

Structure for Countries table
- ID int, autoincrement, primary key
- Name varchar

Structure for Locales table
- CountryID int, primary key
- LocaleID int, primary key
- Name varchar

Handling INSERT - To insert in Countries table, simply populate Name field (or any other fields you may need):

INSERT INTO Countries
  (Name)
VALUES
  ('Ireland')

The ID field will be populated automatically. For this example, we can imagine that "Ireland" will have ID = 1.
- To insert in Locales, you'll pass three values, ie CountryID, LocaleID and Name.

INSERT INTO Locales
  (CountryID, LocaleID, Name)
VALUES
  (1, 1, 'Lorem')

This query will insert LocaleID for the Country with ID = 1 (ie Ireland) and 'Lorem' as a name. To insert 'Ipsum', you'll do the same:

INSERT INTO Locales
  (CountryID, LocaleID, Name)
VALUES
  (1, 2, 'Ipsum')

Where LocaleID will be 2, for Country with ID = 1 and name will be 'Ipsum'.

How to retrieve the data
Since now data is split in two tables, you'll have to use a Join to put it together. It's very simple:

SELECT
  C.ID AS CountryID
  ,L.Name AS CountryName
  ,L.LocaleID
FROM
  Countries C
  LEFT JOIN
  Locales L ON
    (L.CountryID = C.CountryID) AND
    (L.LocaleID = :InputLocaleID)

That's it. Now your query will return the Country with its name in the proper Locale, if it exists. If it doesn't, CountryName and LocaleID will be NULL.

Update 2012/08/11 - How to use a single table (not recommended)

If you wish to use a single table for the Countries, you'll have to handle the Country IDs manually. That is, you'll perform an INSERT as follows:

INSERT INTO Countries
  (ID, LocaleID, Name)
VALUES
  (:CountryID, :LocaleID, :Name)

This, however, will leave you with an issue. Imagine the table contains an unspecified number of Countries and you have to add a new one. What ID would you give to this new Country?

Answer 2

Perhaps some thing like

Locales
(LocalID, LocaleName) Use the standard id e.g. en-GB
Primary Key (LocaleID)

Countries (might have to work on this bit for countries like Belgium (Waloon and Flemish)

(CountryID,CountryLocaleID)
Primary Key (CountryID)
ForeignKey CountryLocaleID -> Locales(LoacleID)

(add any other country specific info, but not the name!

CountryTranslations
(CountryID, LocaleID,InternationalisationID) 
Primary Key(CountryID,LocaleID) 
Unique Key(InternationalisatiosnID)
Foreign Key CountryID -> Countries.CountryID
Foreign Key LocaleID -> Locales.LocaleID
Foreign Key InternationalisationID -> Internationalisations.InternationalisationID

(This is your link between country and it's name in various Locales

Internationalisations
(InternationalsationID, Translation)
PK (InternationalisationID)

(All your translations.)