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Sams Teach Yourself Database Programming with Visual C++ 6 in 21 Days phần 6

BasketballShoes bảng sẽ chứa các lĩnh vực cho lưỡi duy nhất, trên, ren, và archsupport. Bạn cũng sẽ cần phải có một trường bổ sung cho khóa chính trong các Simpo PDF Merge và Split Version Chưa đăng ký - http://www.simpopdf.com BasketballShoes bảng. Bạn cũng nên thêm một thành viên | Teach Yourself Database Programming with Visual C 6 in 21 days .13-Melding Object-Oriented Programming with Relational Databases The BasketballShoes table would contain fields for sole upper tongue laces and archsSimpo PD F MergeandaSplit UnregisterecaVersiori - http www.simpopdf.corrkey in the BasketballShoes table. You should also add a data member to the shoe class to hold the primary key from the database table. If other classes derive from athleticshoe such as crosstrainer you would want to create a CrossTrainers table that contains fields for sole upper tongue laces the primary key and whatever data members are in the crosstrainer class. Sometimes however it might be necessary to get a count all of the shoes. That would mean that you would have to tell the database to count the records in the BasketballShoes table count the records in the CrossTrainers table and add those two numbers together. That would not be very elegant and will become uglier if the number of different types of shoes increases. One possible solution is to create a Shoes table that contains fields for the primary key sole and upper and remove the sole and upper fields from the BasketballShoes table and the CrossTrainers table. You would need to add a field to the Shoes table to indicate the shoe type. The idea then would be to add a record for each shoe to the Shoes table and also add a record to whatever additional table is appropriate. For instance a basketball shoe would have a record in the Shoes table which indicates its sole and upper. It would also have a record in the BasketballShoes table that indicates its tongue laces and archsupport. The Shoes table and the BasketballShoes table would have a one-to-one relationship with each other based on the primary key in each table. Likewise a cross-trainer shoe would have a record in the Shoes table and a record in the CrossTrainers table. The database schema would look like the one shown in Figure 13.4. Figure 13.4 2 A relational database