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  1. #1
    Join Date
    Jul 2011

    Basic database implementation

    I'm pretty new to databases but am trying to implement one for persistent storage in a small python application I'm writing. The application records the loan of access cards to students. I've identified Loan, Card and Student as objects and they map to tables:

    - loan_id (PK),
    - due_date
    - return_date
    - student_id (FK)
    - card_id (FK)

    - student_id (PK)
    - fname
    - sname

    - card_id (PK)
    - active

    Now I just need some pointing in the right direction tightening up the design so I can convert it to python/sqlalchemy code. When a student borrows a card a new loan is created (and a new student and card if they don't already exist). A card can belong to many loans (after a card is returned it can be reused) but a loan can only have one card so card to loan is a one to many relationship. Student to loan is also a one to many relationship as students can have many loans but a loan is only given to one student. Card and student don't have a relationship to each other. When I query the database I am going to have to join the tables on the FKs to get all the data I need to display in the application. Can I do multiple joins?

    This is my understanding of what I need and I am ready to implement it in python code. I am really looking for someone to review the above and check I am correct and have not misunderstood anything. Is the above in 3rd Normal form? (I think it is). Do I have any problems here? Am I fine to join multiple tables?

    Thanks for reading.

  2. #2
    Join Date
    Apr 2002
    Toronto, Canada
    yes, you can do multiple joins

    the design looks fine to me | @rudydotca
    Buy my SitePoint book: Simply SQL

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