How does StumbleUpon store their categories in their Database?

Each user have their own set of chosen categories开发者_JAVA技巧, then only those chosen categories will be shown to the user when they stumble from site to site.

So, my question is this a one to many relationship? Like one user id is connected to many categories in the database?

Then all the categories is stored in one table?

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I've never used StumbleUpon, but here is my guess:

They have a User table, a Category table, and a FavoriteCategory table.

The Category table has an id column and a name column. The User table has an id column, an email column, a username column, etc.

The FavoriteCategory table is where the magic happens!

It has a userId column and a categoryId column. Every time a user adds a new favorite category, a new record is added to the FavoriteCategory table with the user's id as the userId and the category's id as the categoryId. All it takes is a simple INNER JOIN to grab all the data in a single query.

With this schema, users can have an unlimited number of favorite categories! :]

Edit: Try reading about third normal form.