Here's what's wrong with last week's picture, namely:
Q: "I'm currently trying to design a database and I'm not too sure about the best way to approach a dynamically sized array field of one of my objects. My first thought is to use a column in my object to store an array of integers. However the more I read, the more I think this isn't the best option. Concrete example wise, I have a player object that stores 0 to many items, which are represented by an integer. What is the best way to represent this?"
A: "If a collection of values is atomic, store them together. Meaning, if you always care about the entire group, if you never search for nested values and never sort by nested values, then they should be stored together as a single field value. If not, they should be stored in a separate table, each value bring a row, each assigned the parent ID (foreign key) of a record on the other table that "owns" them as a group. For more info, search on the term "database normalization".Focus on physical implementation ("dynamically sized array field") without well-defined conceptual and logical features it is supposed to represent ("a player object" is hardly enough) and confusion of levels of representation (a real world object does not "store" anything) are always a red flag, an indication of poor grasp of foundation knowledge. So let's introduce some.
Some databases, support an array as a data type. For example, Postgres allows you to define a column as a one-dimension array, or even a two dimension array. If your database does not support array as a type of column definition, transform you data collection into an XML or JSON support if your database your database supports that type. For example, Postgres has basic support for storing, retrieving, and non-indexed searching of XML using XPath. And Postgres offers excellent industry-leading support for JSON as a data type including indexed support on nested values. Going this XML/JSON route can be an exception to the normalization rules I mentioned above." --StackOverflow.com