Beginning Microsoft SQL Server 2008 ... - S3 Tech Training

Chapter 8: Being Normal: Normalization and Other Basic Design Issues
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Figure 8-28
You may not have the exact same positions for your table, but the contents should be the same. We’re now
ready to start adding relationships, but we probably ought to stop and think about what kind of relationships
we need.
All the relationships that we’ll draw with the relationship lines in our SQL Server diagram tool are going
to be one-to-zero, one, or many relationships. SQL Server doesn’t really know how to do any other kind
of relationship implicitly. As we discussed earlier in the chapter, you can add things such as unique constraints
and triggers to augment what SQL Server will do naturally with relations, but, assuming you
don’t do any of that, you’re going to wind up with a one-to-zero, one, or many relationship.
The bright side is that this is by far the most common kind of relationship out there. In short, don’t
sweat it that SQL Server doesn’t cover every base here. The standard foreign key constraint (which is
essentially what your reference line represents) fits the bill for most things that you need to do, and the
rest can usually be simulated via some other means.
We’re going to start with the central table in our system — the Orders table. First, we’ll look at any relationships
that it may need. In this case, we have one — it needs to reference the Customers table. This is
going to be a one-to-many relationship with Customers as the parent (the one) and Orders as the child
(the many) table.
To build the relationship (and a foreign key constraint to serve as the foundation for that relationship),
we’re going to simply click and hold in the leftmost column of the Customers table (in the gray area) right
where the CustomerNo column is. We’ll then drag to the same position (the gray area) next to the
CustomerNo column in the Orders table and let go of the mouse button. SQL Server promptly pops
up with the first of two dialogs to confirm the configuration of this relationship. The first, shown in
Figure 8-29, confirms which columns actually relate.
As I pointed out earlier in the chapter, don’t sweat it if the names that come up don’t match with what
you intended — just use the combo boxes to change them back so both sides have CustomerNo in them.
Note also that the names don’t have to be the same — keeping them the same just helps ease confusion
in situations where they really are the same.