Before you start creating any tables, we suggest that you take some extra time to plan out your intended database objects, deciding the names and types for each column for each table, and the purpose of each. This can help you to be consistent with table naming structures, which in turn helps you more easily read and construct "legible" queries and statements.
In addition to this somewhat semantic consideration, it is important to be sure that each table's relationship to each other table is clearly defined. This can be an important point of table design, as you do not wish to redundantly represent large amounts of data, nor do you want to end up omitting important data from one table by misunderstanding the needs that must be satisfied by your implementation.
As an example, consider again the Book Town books table, from Table 3-1 . This table holds an internal Book Town identification number for each book, the title, an author identification number, and a subject identification number. Notice that, rather than storing the name of the author, and rather than storing a text representation of the subject of the book, simple identification integers are stored.
These identification numbers are used to create relationships between two other tables: the authors table, and the subjects table, whose partial contents are shown in Table 3-27 and Table 3-28 .
Table 3-27. The Authors Table
Table 3-28. The Subjects Table
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By keeping the author and subject-specific data separate from the books table, the data is stored more efficiently. When multiple books need to be correlated with a particular subject, only the subject_id needs be stored, rather than all of the data associated with that subject. This also makes for simpler maintenance of data associated with book subjects, such as the location in the store. Such data can be updated in a single, small table, rather than having to update all affected book records with such a modification. The same general principle applies to the authors table, and its relationship to the books table via the author_id .
Thoughtful planning can also help to avoid mistakes in choosing appropriate data types. For example, in the editions table, ISBN numbers are associated with Book Town book identification numbers. At first glance, it might seem that the ISBN number could be represented with a column of type integer . The design oversight in this case would be that not only can ISBNs sometimes contain character data, but a value of type integer would lose any leading zeroes in the ISBN (e.g., 0451160916 ).
For all of these reasons, good table design is not an issue to be overlooked in database administration.