Microsoft SQL Server(Introduction to Databases)

Introduction

A database is primarily a group of computer files that each has a name and a location. Just as there are different ways to connect to a server, in the same way, there are different ways to create a database.

To create a new database in Microsoft SQL Server Management Studio, in the Object Explorer, you can right-click the Databases node and click New Database... This would open the New Database dialog box.

Practical Learning: Creating a Login

Make sure you had created a user account named pkatts introduced in Lesson 1.
To launch Microsoft SQL Server, click Start -> (All) Programs -> Microsoft SQL Server 2008 -> SQL Server Management Studio
On the Connect to Server dialog box, make the correct selections and provide the appropriate information, then click Connect
In the Object Explorer, expand the server name if necessary.
Right-click Security, position the mouse on New, and click Login...
Set the owner to ComputerName\pkatts (Windows XP or Vista) or DomainName\pkatts (Windows Server) (you can also click Search to locate the user name)
Click OK

New Login

The Name of a Database

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].

Practical Learning: Starting the Management Studio

In the Object Explorer, right-click Databases and click New Database...
In the Name text box, type MotorVehicleAdministration

New Database

The Owner of a Database

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:

Select
Database Owner

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.

Practical Learning: Specifying the Database Owner

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)

New Database

The Primary Size of a Database

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.

Practical Learning: Setting the Database File Size

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

Initial Size

The Location of a Database

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:

New Database

Replace it with an appropriate path of your choice.

New Database

Practical Learning: Checking the Location of the Data File

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

New Database

Default Databases

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.

The System Databases

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.

Database Creation With Code

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

Practical
Learning Practical Learning: Creating a Database Using SQL

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

To execute the statement, press F5

The CREATE DATABASE Statement

Using Code Template

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.

Database Maintenance

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.

SQL Server Management Studio

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.

Practical
Learning Practical Learning: Deleting a Database

In the Object Explorer, right-click MotorVehicleAdministration and click Delete
In the Delete Object dialog box, click OK

Deleting a Database Using SQL

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.

Practical
Learning Practical Learning: Deleting a Database With Code

On the Standard toolbar, click the New Query button
To delete a database, type:
```
DROP DATABASE RealEstate1;
GO
```
Press F5 to execute the statement

Database Routines

The Current Database

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;

Refreshing the List of Databases

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.

Schemas

Introduction to Namespaces

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:

Namespace

Notice that there are various types of objects within a namespace.

Introduction to Schemas

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.

Creating a Schema

To create a schema, right-click Schemas and click New Schema...

Object Explorer - 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:

Schema

After providing a name, you can click OK.

We will see a practical example of creating a schema in Lesson 7.

Accessing an Object From a Schema

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