Datasheet

SQL Server is a relational database consisting of many components, each of which contains multiple

objects. In the following sections, you examine the main objects that make up a SQL Server database.

While you will not examine each and every object of a database, rest assured that what you do learn here

will serve you well, laying the foundation for what you will be doing throughout the rest of this book.

A SQL Server database consists of at least two files: a data file and a log file. The data file contains all the

data that makes up a SQL Server database, such as tables, indexes, and stored procedures. You examine

these objects shortly. The log file contains transaction logs, which are records of changes made to the

database.

When you initially create a SQL Server database, the data file and log file are created by SQL Server; the

data file has an

.mdf extension and the log file has an .ldf extension. As your database grows and you

run out of room on the hard drive, your database administrator may create a secondary data file on a

separate hard drive. It will typically have an

.ndf file extension. Creating a secondary data file for a

database typically happens only with large enterprise databases, as most hard drives today can hold

multiple database files on a single drive, given the drives extremely large capacity.

Data files

The data file contains multiple objects that make up a database. Table 1-1 lists the various objects that

make up a database and are contained in the data file. While you will not be exploring each of these

objects in detail, it is helpful to know that they exist and what they do.

Table 1-1: SQL Server Data File Objects

Object Description

Tables Contains the data in a database, organized in a row-column

format.

Keys Primary keys provide a unique value for each row of data in a

table. Foreign keys provide a relationship between two tables

using a column in one table and the primary key in another table.

Indexes Provides pointers to rows in a table in a similar fashion that the

index in this book provides pointers to specific topics.

Constraints Provides a means by which you can enforce the integrity of a

database, such as not allowing a column to contain a NULL value.

Stored Procedures A single SQL statement or group of SQL statements

compiled into a single execution plan.

Views A SQL SELECT statement that returns a virtual table.

Triggers A special class of stored procedures that are automatically

executed when an

Insert, Update, or Delete statement

is executed against a table.

Defaults A default value that is inserted into a column in a table when no

value is supplied.

Chapter 1

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