Bill Karwin
Programmers commonly use comma-separated lists to avoid creating an intersection table for a many-to-many relationship. I call this antipattern Jaywalking, because jaywalking is also an act of avoiding an intersection. (Location 439)
Your application may need the data in a comma-separated format and have no need to access individual items in the list. Likewise, if your application receives a comma-separated format from another source and you simply need to store the full list in a database and retrieve it later in exactly the same format, there’s no need to separate the values. Be conservative if you decide to employ denormalization. Start by using a normalized database organization, because it permits your application code to be more flexible, and it allows your database to help preserve data integrity. (Location 594)