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This is an excellent question, according to my experience, in ERD diagrams and relational databases direction is implied. In RDBMS you always define Many-To->One (trivial case One-To->One) relationships. The Many side of the relationship, a.k.a children, references the One side, a.k.a parent and you implement this with a Foreign Key constraint. ...


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This is an excellent question, according to my experience, in ERD diagrams and relational databases direction is implied. In RDBMS you always define Many-To->One (trivial case One-To->One) relationships. The Many side of the relationship, a.k.a children, references the One side, a.k.a parent and you implement this with a Foreign Key constraint. ...


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In a relational database every table should have a Primary Key. A Primary Key can be one column, like StudentId, or it can be a Compound Key, like (StudentID, CourseID), which is exactly what you should use for Exam. Then Exam's Primary Key guarantees that "a student can't get multiple grades for a single course", because that would require ...


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You would create a unique constraint on exam (StudentId, CourseId) this would usually be achieved with a unique index on that table that covered the two columns. Here's a quick demo in MySql


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None of Codd's rules live in isolation. They all work together to give you that wonderful experience you have today with modern RDBMS, which we all take for granted today. Because before Codd's rules, the world was a horrible horrible place that we "youngsters" didn't know and the "elders" desperately try to forget. Just imagine that ...


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This would be a case for either filtering the data during your query (WHERE clause) or creating a view that already filters it out. In normal practice, a person table is a person table, and unless the fundamental fields are different (like the difference between customers and employees), then all person records go into the same table, and the diagrams ...


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Metadata isn't uniquely more important than non-metadata in this context. Rather, his rule just simply wants the reader to realize that "All Information" is inclusive of even the metadata regarding the database itself. This is useful for understanding the structure of the database and the relational model behind it. This is why the Information ...


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