Keys and Joins
In the previous discussions, I used terms such as primary key and join. These are important database terms. As you know, a database consists of a series of related entities. These entities will model the tables that will hold the data. The attributes that you will extract from the database will most likely be contained in several tables. A join is the process of matching records from one table to another. The entity relationships show you the entities (tables) that can be joined.
The database keys are the tools used to match the records from two different tables. Records are matched by having a common value(s) in one or more columns in the related tables. For example, suppose that the database has two tables: Departments and Employees. ...
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