Datasheet

Then you would add the foreign key, in the form of another constraint:

ALTER TABLE [dbo].[Product] WITH CHECK ADD CONSTRAINT [FK_Product_ProductCategory]

FOREIGN KEY ([ProductCategoryId])

REFERENCES [dbo].[ProductCategory] ([ProductCategoryId])

Here the FK_Product_ProductCategory foreign key is added, linking the

Product.ProductCategoryId column with the ProductCategory.ProductCategoryId column.

There are several

CREATE statements in the SQL vocabulary, each of which has a corresponding ALTER

statement and also a corresponding DROP statement. Dropping an object means deleting it from the

DBMS. This operation doesn’t use the

DELETE keyword, which is used for deleting data; mixing up these

commands is potentially disastrous.

Although this chapter introduces a number of commands, you are far more likely to carry out these

operations via a GUI for day-to-day use. That’s fine, because making even simple mistakes with queries

of this sort can cause irreparable damage.

The most useful thing about these statements so far is that they can be combined together into script

files. Script files can be extremely useful for automating lengthy tasks, and the first place you will see

one of these in action is in the next chapter. You will execute a SQL script file that creates the database

that you will be using for examples throughout the book. The script file contains a complete database,

including multiple tables, table data, and other database objects. If you were to add all of this by hand it

would take a long time indeed, but executing a script takes hardly any time at all.

XML

As noted earlier, XML is a text-based format for the storage of data. It consists of two features: data and

markup. Because it is “just” text, it can be read and understood on just about any computer system in

existence, and its well-defined format makes it easy to process. It is also possible to define vocabular-

ies — that is, systems of markup unique to an application or shared among many applications. As such,

XML has become the universal language of choice for the interchange of information between disparate

systems.

In the .NET Framework, XML is used extensively. For example, configuration files for all manner of

applications are written in XML, which makes it easy to edit configurations by hand or programmati-

cally using simple techniques. A rich set of types is defined by .NET to make it easy to manipulate XML

data in various ways. XML is also the basis of SOAP (Simple Object Access Protocol), the underlying

technology that makes web services both possible and platform-independent.

The rise of XML has continued unabatedly for several years, and knowledge of XML is now an essential

part of pretty much any area of computing. This applies to databases, too, and many DBMSes (including

SQL Server) now include tools for dealing with, consuming, and generating XML data.

The XML Format

This section cannot detail every aspect of the XML syntax, but it is a brief summary to reinforce the basic

concepts of XML. After all, the chances are that you will have come across XML before, and if you

haven’t, there are a huge number of excellent resources, in web and print form, to get you started.

Chapter 1

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