Relationships
Although tables are certainly the primary component of a relational database, it's the relationships between the tables that make the database so powerful. After all, if you couldn't establish relationships between tables, the database would be nothing but a simplified spreadsheet program. As it is, however, you can create relationships between tables by relating groups of keys together. There are three types of database relationships: one-to-one, one-to-many, and many-to-many.
The term relationship can refer to a relationship that the database knows about, or it can refer to a conceptual relationship that you might know about but the database does not. When you tell the database about a relationship, it automatically enforces ...
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