Storing arrays in MySQL?

Question

On the Facebook FQL pages it shows the FQL table structure, here is a screenshot below to show some of it (screenshot gone).

You will notice that some items are an

Answer 1

I guarantee you that Facebook is not storing that data in arrays inside their database.

The thing you have to realize about FQL is that you are not querying Facebook's main data servers directly. FQL is a shell, designed to provide you access to basic social data without letting you run crazy queries on real servers that have performance requirements. Arbitrary user-created queries on the main database would be functional suicide.

FQL provides a well-designed data return structure that is convenient for the type of data that you are querying, so as such, any piece of data that can have multiple associations (such as "meeting_for") gets packaged into an array before it gets returned as an API result.

As other posters have mentioned, the only way to store a programming language structure (such as an array or an object) inside a database (which has no concept of these things), is to serialize it. Serializing is expensive, and as soon as you serialize something, you effectively make it unusable for indexing and searching. Being a social network, Facebook needs to index and search almost everything, so this data would never exist in array form inside their main schemas.

Usually the only time you ever want to store serialized data inside a database is if it's temporary, such as session data, or where you have a valid performance requirement to do so. Otherwise, your data quickly becomes useless.