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  1. #1
    Join Date
    Apr 2014

    Unanswered: ER-Diagram Relationships


    In the show entity, why is it necessary to have all those foreign key? Why not we just include them as 1 attribute? For example, we use Cinema_name as the attribute replacing Cinema_ID, would it be okay?

    Another example is why not we use Movie_name as the attribute of the show entity and we no need to include movie_id in the above erd?

    Thanks for your guides!
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  2. #2
    Join Date
    Mar 2009
    Provided Answers: 15
    1. An ID column defined as an AutoNumber (Movie_ID) cannot be changed while another column (say Movie_name) can be edited. This guarantees the integrity of the database.

    2. A function that performs comparisons on Long Integers (Movie_ID) is faster than a function that must compare strings (Movie_Name). This increases the performance of the system.

    Notice that having an Identity (Autonumber) column in a table does not necessarily implies that this column must be the primary key, although it often is. There is also the old debate (war?) about Natural Keys vs Surrogate Keys, but I won't go there!
    Have a nice day!

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