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I am a newbie when it comes to database design. I was trying to create a blogging application and I ran into a problem. My database consists of the following tables:

User
HasInt (Records which user has which interest)
Interest (category of blogs: Sports, Literature etc)
Follow (Records which user follows which user)
Blog
Comment

From what I realise, I should not have anything to do with knowing how many comments have been made for any particular Interest. But I can see that there is a many to one relationship between Comment and Interest. Should I still record this information ? If so, why ?

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    Start by drawing a high-level diagram of how the entities relate, and write out the relations like this: User has zero to many interests, user writes zero to many blogs,user comments on zero to many blogs etc. If there is no direct relation from comment to interest (although an indirect relation may occur through user) there is no relationship that needs to be defined in your model or diagram.
    – user212533
    Commented Jul 21, 2020 at 12:56

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Second what @bbaird says. I usually start with the objects I'll be dealing with. (user, category, blog, comment).

Then I'll start thinking about how they are connected.

  • A user is interested in zero to many categories
  • A user can follow another user
  • A user can create a blog
  • A user can create a comment
  • A comment is applied to a blog
  • A blog belongs to a category

To cover the links that are to one to many or many to many, I'll use joining tables that look like this; UserToCategory (PK int, UserID int, CategoryID int) UserToBlog (PK int, UserID int, BlogID int)

Obviously there's a bit more to fully flesh out the plan, but this gets things started. If your foreign keys are built right, you can run a query to get all comments where the blog category is sports, joining across a couple of tables at once.

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