Relational Database Principles

Summary

In this chapter, we considered how a single database table is much like a single spreadsheet, with four important differences:

• All items in a column must have the same type.

• The number of columns must be the same for all rows in a table.

• It must be possible to uniquely identify each row.

• There is no implied row order in a database table, as there would be in a spreadsheet.

We have seen how we can extend our database to multiple tables, which lets us manage many-to-one relationships in a simple way. We gave some informal rules of thumb to help you understand how a database design needs to be structured. We will come back to the subject of database design in a much more rigorous fashion in later chapters.

We have also seen how to work around many-to-many relationships that turn up in the real world, breaking them down into a pair of one-to-many relationships by adding an extra table.

Finally, we worked on extending our initial database design so we have a demonstration database design, or schema, to work with as the book progresses.

In the next chapter, we will see how to get the PostgreSQL up and running on various platforms.