Mastering Business Analysis with Crystal Reports 9 (Wordware Applications Library)
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The following entity-relationship model displays the different relationships between the tables of the xtreme.mdb database. These relationships utilize primary keys, which contain the following restrictions:
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The value of the primary key must contain a unique value. In other words, no two different rows within a table can have the same value within the primary key field.
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The value of the primary key cannot contain a NULL value. A NULL value represents missing, unknown, or inapplicable data. A NULL value is not the same thing as a zero value.
Entity-relationship models are especially useful when linking multiple tables together for use within a report. Remember, when linking tables together in Crystal Reports, the linking relationships must match the relationships of the tables within the database. An entity-relationship model will tell you how different database tables link together.
The following diagram summarizes the referential integrity constraints required by the tables of the xtreme.mdb database.
| Note | In the xtreme.mdb database, the Financials table does not contain any links to any other tables. |
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