Probably the most important concept that needs to be fully understood before any Relational Database Design can take place is resolving many to many relationships.
These relationships are ‘real world’ things that you have to design into your database. I have had so many discussions with developers who for some unknown reason think it is inefficient to add a link entity into their database design model. It is not only efficient it is vital for a correctly functioning model.
You can find out how to Resolve many to many relationships in our SQL Language Tutorial - Resolving many to many and in our Database Design Tutorial - Resolving many to many. Both pages have the same title, wierd! But they both have different information relevant to the tutorial that they live in.
Of course you could attend our Database Design Course and learn how to build a real-world database.