Probably the most important requirement of creating a
database is to give it a name. The SQL is very
flexible when it comes to names. In fact, it is very less restrictive than
most other computer languages. Still, there are rules you must follow when naming the objects in
your databases:
- A name can start with either a letter (a, b, c, d, e, f, g, h, i, j,
k, l, m, n, o, p, q, r, s, t, u, v, w, x, y, z, A, B, C, D, E, F, G,
H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, or Z), a digit
(0, 1, 2, 3, 4, 5, 6, 7, 8, or 9), an underscore (_) or a non-readable
character. Examples are _n, act, %783, Second
- After the first character (letter, digit, underscore, or symbol),
the name can have combinations of underscores, letters, digits, or
symbols. Examples are _n24 or act_52_t
- A name can include spaces.
Example are c0untries st@ts, govmnt (records), or gl0b#
$urvey||
Because of the flexibility of SQL, it can be difficult
to maintain names in a database. Based on this, there are conventions we
will use for our objects. In fact, we will adopt the rules used in C/C++,
C#, Pascal, Java, and Visual Basic, etc. In our databases:
- Unless stated otherwise (we will mention the exceptions, for example
with variables, tables, etc), a name will start with either a letter (a, b, c, d, e, f, g, h, i,
j, k, l, m, n, o, p, q, r, s, t, u, v, w, x, y, z, A, B, C, D, E, F,
G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, or Z) or an
underscore
- After the first character, we will use any combination of letters,
digits, or underscores
- A name will not start with two underscores
- If the name is a combination of words, at least the second word will
start in uppercase. Examples are Countries Statistics, Global
Survey, _RealSport, FullName, or
DriversLicenseNumber
After creating an object whose name includes space, whenever
you use that object, include its name between [ and ]. Examples are [Countries Statistics],
[Global
Survey], or [Date of Birth]. Even if you had created an
object with a name that doesn't include space, when using that name, you can
still include it in square brackets. Examples are [UnitedStations], [FullName],
[DriversLicenseNumber], and [Country].
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 Practical
Learning: Starting the Management Studio
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- In the Object Explorer, right-click Databases and click New Database...
- In the Name text box, type MotorVehicleAdministration
Whenever a new database is created, the server wants to keep
track of who created that database. This is known as the database owner. By
default, Microsoft SQL Server creates a special account named dbo (for database
owner). When you create a database but do not specify the owner, this account is
used. The dbo account is also given rights to all types of operations that can
be performed on the database. This is convenient in most cases. Still, if you
want, you can specify another user as the owner of the database. Of course, the
account must exist, which means you should have previously created it or you can
use an existing one.
To visually specify the owner of a database you are
creating, you can click <default> in the Owner text box, type the name of
the domain, followed by the back slash, and followed by the user name who
will own the database. Alternatively, you can click the ellipsis button on the right side of the Owner text box.
This would open the Select Database Owner dialog box:
In the Enter the Object Names to Select dialog box, enter
the full name or the username of the user to whom you want to assign the
database. After doing that, click Check Names. If the name is right, the dialog
box would accept it. If the name is not right, you would receive an error. You
can click the Browse button. This would open the Browse For Objects dialog box.
If you see the user object you want to use, click its check box and click OK.
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Practical
Learning: Specifying the Database Owner
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- In the Owner dialog box, click <default> and type DomainName\pkatts
(replace DomainName with the name of your domain; otherwise, skip this step)
(you can also click the browser button on the right side of Owner to locate
and select the desired username)
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The Primary Size of a Database
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When originally creating a database, you may or may not know
how many lists, files, or objects the project would have. Still, as a user of
computer memory, the database must use a certain portion, at least in the
beginning. The amount of space that a database is using is referred to as its
size. If you use the New Database dialog box, after specifying the name of the
database and clicking OK, the
interpreter automatically specifies that the database would primarily use 2MB.
This is enough for a starting database. Of course, you can either change this
default later on or you can increase it when necessary.
If you want to specify a size different from the default, if
you are using the New Database to create your database, in the Database Files
section and under the Initial Size column, change the size as you wish.
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Practical
Learning: Setting the Database File Size
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- In the Database Files section, click the box under the Initial Size
column header, click the up arrow of the spin button and increase its value
to 5
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The Location of a Database |
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As you should be aware of already from your experience on using
computers, every computer file must have a path. The path is where the file is
located in one of the drives of the computer. This allows the operating system to know
where the file is, so that when you or another application calls it, the
operating system would not be confused.
By default, when you create a new database, Microsoft SQL Server
assumes that it would be located at Drive:\Program Files\Microsoft SQL Server\MSSQL10.MSSQLSERVER\MSSQL\DATA folder. If you use the
New Database dialog box of
the SQL Server Management Studio, if you specify the name of the database and click OK, the interpreter automatically creates a new file, and appends the .MDF extension to the file: this is
the (main) primary data file of your database.
If you do not want to use the default path, you can change
it. If you are using the New Database dialog box, to change the path, under the
Path header, select the current string:
Replace it with an appropriate path of your choice.
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Practical
Learning: Checking the Location of the Data File
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- Scroll to the right side and, under the Path header, notice the location
of the file
- Start Windows Explorer
- In the left frame, click the C: drive
- Right-click a blank area in the right frame -> New -> Folder
- Type Microsoft SQL Server Database Development as the name of the
new folder
- Return to the New Database dialog box.
Under Path, click the browse button 
- Locate the Microsoft SQL Server Database Development folder you created
and select it
- Do the same for the other path
- Click OK
When you install Microsoft SQL Server, it also installs 4
databases named master, model, msdb, and tempdb. These databases will be
for internal use. This means that you should avoid directly using them, unless
you know exactly what you are doing.
One of the databases installed with Microsoft SQL Server is
named master. This database holds all the information about the server on which
your MS SQL Server is installed. For example, we saw earlier that, to perform
any operation on the server, you must login. The master database identifies any
person, called a user, who accesses the database, about when and how.
Besides identifying who accesses the system, the master
database also keeps track of everything you do on the server, including creating
and managing databases.
You should not play with the master database; otherwise you
may corrupt the system. For example, if the master database is not functioning right, the system would not work.
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Database Creation With Code |
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To assist you with creating and managing databases,
including their object, you use a set of language tools referred to as the Data
Definition Language (DDL). This most includes commands. For example, the primary
command to create a database uses the
following formula:
CREATE DATABASE DatabaseName
To assist you with writing code, in the previous
lessons, we saw that you could use the query window.
The CREATE DATABASE (remember that SQL is not
case-sensitive) expression is
required. The DatabaseName factor is the name that the new database
will have. Although SQL is not case-sensitive, you
should make it a habit to be aware of the cases you use to name your
objects. Every statement in SQL can be
terminated with a semi-colon. Although this is a requirement in many
implementations of SQL, in Microsoft SQL Server, you can omit the
semi-colon. Otherwise, the above formula would be
CREATE DATABASE DatabaseName;
Here is an example:
CREATE DATABASE NationalCensus;
This formula is used if you do not want to provide any
option. We saw previously that a database has one or more files and we saw where
they are located by defauft. We also saw that you could specify the location of
files if you want. To specify where the primary file of the database will be
located, you can use the following formula:
CREATE DATABASE DatabaseName
ON PRIMARY
( NAME = LogicalName, FILENAME = Path )
The only three factors whose values need to be changed from
this formula are the database name that we saw already, the logical name, and
the path name. The logical name can be any one-word name but should be different
from the database name. The path is the directory location of the file. This
path ends with a name for the file with the extension .mdf. The path should be
complete and included in single-quotes. Here is an example:
CREATE DATABASE NationalCensus
ON PRIMARY
( NAME = DataRepository, FILENAME = 'C:\Exercises\NationalCensus.mdf')
GO
Besides the primary file, you may want to create and store a
log file. To specify where the log file of the database would be located, you
can use the following formula:
CREATE DATABASE DatabaseName
ON PRIMARY
( NAME = LogicalName, FILENAME = Path.mdf )
LOG ON
( NAME = LogicalName, FILENAME = Path.ldf )
The new factor in this formula is the path of the log file.
Like the primary file, the log file must be named (with a logical name). The
path ends with a file name whose extension is .ldf. Here is an example:
CREATE DATABASE NationalCensus
ON PRIMARY
( NAME = DataRepository, FILENAME = 'C:\Exercises\NationalCensus.mdf')
LOG ON
( NAME = DataLog, FILENAME = 'C:\Exercises\NationalCensus.ldf')
GO
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Practical
Learning: Creating a Database Using SQL
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- To open the code editor, in the Object Explorer, right-click the name of
the server and click New Query
- In the empty window, type:
CREATE DATABASE RealEstate1
ON PRIMARY
( NAME = DataRepository, FILENAME = 'C:\Microsoft SQL Server Database Development\RealEstate1.mdf')
LOG ON
( NAME = DataLog, FILENAME = 'C:\Microsoft SQL Server Database Development\RealEstate1.ldf')
GO
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- To execute the statement, press F5
To specify more options with code, Microsoft SQL
Server ships with various sample codes you can use for different
assignments. For example, you can use sample code to create a database.
The sample codes that Microsoft SQL Server are accessible from the
Template Explorer.
To access the Template Explorer, on the main menu,
you can click View -> Template Explorer. Before creating a database,
open a new query window. Then:
- To create a new database using sample code, in the Template Explorer,
expand the Databases node, then drag the Create Database node and drop it in
the query window. The new database would be created in the server that holds
the current connection
- If you have access to more than one server, to create a database in
another server or using a different connection, in the Template Explorer,
expand the Databases node, right-click Create Database and click Open. In
the Connect to Database Engine dialog box, select the appropriate options,
and can click OK
With any of these actions, Microsoft SQL Server would
generate sample code for you:
-- =============================================
-- Create database template
-- =============================================
USE master
GO
-- Drop the database if it already exists
IF EXISTS (
SELECT name
FROM sys.databases
WHERE name = N'<Database_Name, sysname, Database_Name>'
)
DROP DATABASE <Database_Name, sysname, Database_Name>
GO
CREATE DATABASE <Database_Name, sysname, Database_Name>
GO
You would then need to edit the code and execute it
to create the database. From the previous lessons and sections, we have
reviewed some characters uch as the comments -- and some words or
expressions such as GO, CREATE DATABASE, and SELECT.
We will study the other words or expressions in future lessons and
sections.
If you have created a database but don't need it anymore, you can
delete it. It is important to know, regardless of how you create a
database, whether using SQL Server Management Studio, code in the query
window, or the Command Prompt, every database can be accessed by
any of these tools and you can delete any of the databases using any of
these tools.
As done with creating a database, every tool provides
its own means.
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SQL Server Management Studio |
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To delete a database in SQL Server Management Studio,
in the Object Explorer, expand the Databases node, right-click the
undesired database, and click
Delete. A dialog box would prompt you to confirm your intention. If you
still want to delete the database, you can click OK. If you change your
mind, you can click Cancel.
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Practical
Learning: Deleting a Database
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- In the Object Explorer, right-click MotorVehicleAdministration and click Delete
- In the Delete Object dialog box, click OK
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Deleting a Database Using SQL |
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To delete a database in SQL Query Analyzer, you use the DROP DATABASE
expression followed by the name of the database. The formula used is:
DROP DATABASE DatabaseName;
Before deleting a database in SQL, you must make sure
the database is not being used or accessed by some one else or by another
object.
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Practical
Learning: Deleting a Database With Code
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- On the Standard toolbar, click the New Query button
- To delete a database, type:
DROP DATABASE RealEstate1;
GO
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- Press F5 to execute the statement
While writing code in a Query Window, you should
always know what database you are working on, otherwise you may add code
to the wrong database. To programmatically specify the current
database, type the USE keyword followed by the name of the database.
The formula to use is:
USE DatabaseName;
Here
is an example:
USE GovernmentStatistics;
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Refreshing the List of Databases |
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Some of the windows that display databases, like the SQL Server Management Studio, don't update their list immediately if an
operation occurred outside their confinement. For example, if you create a
database in the query windows, its name would not be updated in the Object
Explorer. To view such external changes, you
can refresh the window that holds the list.
In SQL Server Management Studio, to update a list,
you can right-click its category in the Object Explorer and click Refresh. Only
that category may be refreshed. For example, to refresh the list of
databases, in the Object Explorer, you can right-click the Databases node
and click Refresh.
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Introduction to Namespaces |
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A namespace is a technique of creating a series of items
that each has a unique name. For example, if you start creating many databases,
there is a possibility that you may risk having various databases with the same
name. If using a namespace, you can isolate the databases in various namespaces.
In reality, to manage many other aspects of your database server, you use
namespaces and you put objects, other than databases, within those namespaces.
Therefore, a namespace and its content can be illustrated as follows:
Notice that there are various types of objects within a
namespace.
Within a namespace, you can create objects as you wish. To
further control and manage the objects inside of a namespace, you can put them
in sub-groups called schemas. Therefore, a schema is a group of objects within a
namespace. This also means that, within a namespace, you can have as many
schemas as you want:
Notice that, just like a namespace can contain objects
(schemas), a schema can contain objects also (the objects we will create
throughout our lessons).
To manage the schemas in a namespace, you need a way to
identify each schema. Based on this, each
schema must have a name. In our illustration, one schema is named Schema1.
Another schema is named Schema2. Yet another schema is named Schema_n.
A schema is an object that contains other objects. Before
using it, you must create it or you can use an existing schema. There are two types of schemas you can use, those built-in
and those you create. When Microsoft SQL Server is installed, it also creates a
few schemas. One of the schemas is called sys.
The sys schema contains a
list of some of the objects that exist in your system. One of these objects is
called databases (actually, it's a view). When you create a database, its
name is entered in the databases object using the same name you gave it.
To access the schemas of a database, in the Object Explorer,
expand the Databases node, expand the database that will hold or own the schema,
and expand the Security node.
To create a schema, right-click Schemas and click New
Schema...
This would open the Schema - New dialog box. In the Schema
Name text box, enter a one-word name. Here is an example:
After providing a name, you can click
OK.
We will see a practical example of creating a schema
in Lesson 7.
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Accessing an Object From a Schema |
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Inside of a schema, two objects cannot have the same name,
but an object in one schema can have the same name as an object in another
schema. Based on this, if you are accessing an object within its schema, you can
simply use its name, since that name would be unique. On the other hand, because
of the implied possibility of dealing with objects with similar names in your
server, when accessing an object outside of its schema, you must qualify it. To
do this, you would type the name of the schema that contains the object you want
to use, followed by the period operator, followed by the name of the object you
want to use. From our illustration, to access the Something1 object that belongs
to Schema1, you would type:
Schema1.Something1
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Exercise: Utility Company |
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- Using Microsoft SQL Server Management Studio, create a database named
UtilityCompany1 (Accept the default settings)
- Perform some research on the Internet to find out about different regions
of the United States. On a piece of paper, create a list of the regions of
the US
- Connect to the server from the Command Prompt
- From the Command Prompt, create a database named UnitedStatesRegions1
- Exit the Command Prompt
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