Build Your Own ASP.NET 2.0 Web Site Using C# & VB, Second Edition

want to allow is the same pair of values to appear in the table twice (it wouldn’t

make sense to associate a particular employee with a particular department more

than once). For this reason, we usually create mapping tables with a multi-column

primary key.

In this example, the primary key for the EmployeeDepartment table would consist

of the EmployeeID and DepartmentID columns. This enforces the uniqueness

that is appropriate to a look-up table, and prevents a particular employee from

being assigned to a particular department more than once.

If you’d like to learn more about many-to-many relationships, or about anything

else related to SQL Server programming, I recommend you download and use

the product’s excellent documentation, SQL Server Books Online.

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Summary

This chapter has introduced the fundamental concepts of relational databases.

You learned about the underlying structure of a modern relational database,

which is composed of tables, columns, and rows, and about crucial concepts that

can aid in database performance, maintenance, and efficiency. You’ve also learned

how to implement and enforce table relationships, and you have a solid under-

standing of good relational database design.

Chapter 8 goes beyond data storage and introduces you to the language used to

access and manipulate the data you hold in your tables. That language is the

Structured Query Language, or SQL.

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http://msdn2.microsoft.com/en-us/library/ms130214.aspx

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Chapter 7: Database Design and Development