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Database Systems

Introduction to the Structured Query Language

Harmony Kwawu

hkwawu@aol.com

Course Outline

� Introduction

� Use of database applications

� Database Management System

� Relational operators

� Purpose of relational database query

� SQL Commands:

� Data manipulation command

� Data definition command

� SQL Joins

� Summary

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Introduction

� Our world depends on data and increasingly so, in order to thrive. There are many different methods used for storing data but the idea of relational database technology has proved the most advantageous

� A key benefit of relational database approach is the capacity to allow users to retrieve data from or interact with database in an intuitive and variant ways.

� At the heart of all major relational database approach is the SQL, standing for Structured Query Language. SQL is based on set theory or relational principles.

� Relational operators help developers write complex procedures toenforce business rules and enhance database interactivity

� There are six different types of relational operators used in major DBMS as illustrated in this brief introduction to the Structured Query Language

But first ….

Uses of Database Applications

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Uses of Database Applications

• Databases are the backbone of all information systems. Examples of

information system types include:

• Patient appointment systems

• Library customer registration and account management systems

• Automatic Teller Machine (ATM)

• Hotel reservation and bookings

systems

• Stock control systems, and

• School information mgt systems (SIMS)

Relational Database Systems

Relational Database Systems

� There are different ways to store data. Data can be stored in files, documents, image and sound forms etc

� But relational database approach is the most versatile and convenient

� Relational database approach is one in which data is organised into sets or tables

� Where each table is linked to other tables to form a relational model.

STUDENT

Student_ID (PK)

StudentName

StudentAddress

Email

Telephone

Comment

Course_Code(FK)

Module Module

Module_Id(PK)

Module Name

Aim

Outcome

Course_Code (FK)

Course_Code(PK)

CourseName

CourseDescription

Course Course

A simple illustrated example of relational data model.

Relations

� Tables in a relational database are technically referred to as entities or relations.

Key Components

� The main components of relational database systems are:

� The database or data repository consisting of:

� Individual tables linked to form a logical model

� Attributes of stored data

� Specific values or records

� Database Manager (BM)

� The command base for retrieving and managing the database (SQL)

� Applications for interacting with the content of the data base

� User interface

Major benefits of Relational database systems

� Relational database approach also allow data from different parts of an organisation to be stored in one place

� This approach makes it easy to protect and control access to the database

� Also, storing data in a logically related tables can be accessed by different applications and users according to their needs

SQL

What is Database Management System

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Database Management System (DBMS)

� A database management system (DBMS) is a large piece of software that is used in defining, creating, updating and deleting a database records.

� A database management system is also known as database manager

� It supports the operation of database applications within an integrated, controlled and accessible framework.

� Examples of DBMS are:

� MS Access

� Oracle PL/SQL

� MySQL

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A simple Infographics of Database Management Systems

Data Base Query

Relational Database Operators

Operators are generally used in programming and application development to build expressions.

� There are generally four categories of operators, namely: � Arithmetic operators � Relational or Boolean Operators � Logical Operator � Assignment Operator

� Relational operators are the most common type of operators used in relational database

� They are used to help write complex procedures to enforce business rules and construct query statements

Data Base Query

Database Relational Operators

Common Database Relational Operators

OperatorOperatorOperatorOperator MeaningMeaningMeaningMeaning ExampleExampleExampleExample= Equal to Gives exact value in a database

<> Not equal to List values other than the one specified

> Greater than List values that are greater than the one specified

< Less than Shows values that are less than the one stated

<= Less than or equal to Shows values stated and all values less than the one stated

>= Greater than or equal to Shows values specified and all values greater than the one stated

Other Database Relational Operators Cont..

OperatorOperatorOperatorOperator MeaningMeaningMeaningMeaning ExampleExampleExampleExampleBetween ......> And <..... Retrieve all values within the

given range excluding the two values stated

Between Between Retrieve all values within the given range including the two values stated

OR ......OR ...... List one set of value or another

The SQL Command

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The SQL command

� We shall examine in future posts how the above operators are used to programme relational database,

� But first let’s discuss other aspect of database query-the SQL command.

� As noted above, SQL allow database users to retrieve data, update existing records, delete records, create index, create new tables and delete tables

� SQL statements can be interactive and embedded in third party programming languages, such as ASP.NET or PHP

� And SQL statement may be simple or complex, more on this in future

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SQL Command

� In MS Access database management systems for example, queries are created using what is known as Access Query Design view.

� The queries created in design view can be viewed and edited to reflect changes

� It’s equally possible to write new query statements directly in SQL view

� Note that SQL Stand for structured query language and that SQL is the defector programming language for relational

databases.

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Illustrated Example: Query Design View

A very simple query

A local bank require the design of a system to store record of its clients

and the loan they borrow. The system should be able to store details of the clients, details of loan and loan types and the branch for Each customer. A preliminary entity relation model has been produced by one

of your database development team member as shown below: use theERD to produce the following queries

Bank customer loan processing system challenge

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Illustrated Example: Query Design View

Bank Database Model

A slightly complex query

SQL View in MS Access

SQL Query statement

SQL Command Types

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SQL Command Types

� There are many categories of structured Query Language statements.

� For our purpose, we shall focus on two key categories as follows:

� The data definition language (DDL) commands, and

� Data manipulation language (DML) commands

DDL and DML

� Data Definition Language (DDL)

� Are used to define and model the structure of data

� e.g. Create the database, Alter (make changes to the database) and Drop (delete database object)

� Data Manipulation Language (DML)

� Used mainly for interacting and manipulating stored data

� e.g. Select, Update, Delete and Insert new records into database

Data Definition Language (DDL)

� Create statement

� Alter statement, and

� Drop statement

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Example 1: SQL Create Table Command

Create Table Staff(

Staff_Id Number (10) NOT Null Staff_FirstName Varchar(30)

NOT Null,

Staff_SurName Varchar(30) NOT Null,

Staff_Position Varchar(10) NOT Null,

Staff_EmailVarchar(30) NOT Null,

Staff_Telephone Varchar(30) NOT Null,

Room_Number Varchar(30) NOT Null,

Staff_Speciality Varchar(30) NOT Null,

Constraints Staff_PK Primary Key (Staff_id));

The Result

� See if you can guess the result by sketching it

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Example2: SQL Create Table Cont..

� Create Table Course (

Course_Code Number (10) NOT Null,

Course_Name Varchar(30) NOT Null,

Course_Aim Varchar(30) NOT Null,

Course_Description Varchar(100) NOT Null,

Staff_Id Number (30),

Constraints Course_PK Primary Key (Course_Code),

CONSTRAINTS Staff_FK FOREIGN (Staff_Id),

REFERENCES Staff(Staff));

The Result

� Again, see if you can guess the result by sketching it

Other important DDL Statements

Other important DDL Statements

� Alter statement and Drop statement

� Find out more from the link below:

http://www.w3schools.com/sql/sql_alter.asp

Data Manipulating Language

Data Manipulating Language

Select statement is perhaps the most important and

frequently used data manipulation statement.

Other equally important commands are:

� Update command

� Delete command

� Insert command

� The main purpose of DML, is to allow database users to retrieve (select) and or manipulate stored data

Structure of select statement

� Below are what could be descried as the building blocks of simple select command:

� SELECT

� FROM

� Where

� Or

Quiz

� Briefly describe what Each of the following select statement keywords means in practice?

� SELECT

� FROM

� Where

� Or

Example of select statement:

� List the names and email address of all staff in room 123

� SELECT (Staff_ID, First Name, Surname, Email, Telephone, Room

� FROM Staff,

� WHERE ((Room)=123));

The Result

� See if you can guess the result by sketching it

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Data Manipulating Language

� Example of DML select statement-2:

� List Name and detail of students

� SELECT Student_ID, First_Name, Surname, Email, Mobile, Home_Tel

� FROM Student;

The Result

� See if you can guess the result by sketching it

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DML SQL Command

� List names of students and their course

� SELECT Student_ID, First_Name, Surname, D_O_B, Email,Course_Name, Description

� FROM Course INNER JOIN Student ON tblCourse.Course_ID=TblStudent.Course_ID;

The Result

� Congratulation if you were able to guess the result correctly by sketching it

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Other Types of DML Query

Update Query in MS Access:

Example 1:

� UPDATE TblStudent SET TblStudent.First_Name = "Null", TblStudent.Surname = “Null”, TblStudent.D_O_B = “Null”;

Example 2:

� UPDATE TblJob_Type SET TblJob_Type.Charges = “£90";

� Log on to the URL below to find out more:

� http://www.w3schools.com/sql/sql_update.asp

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Delete Query in MS Access

Delete all record from the Module Table

DELETE *

FROM TblModules;

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Insert data into table

� INSERT INTO Student (Student_Name,Student_Address,Email)

Values (Joe Williams, London Road, JW@Yahoo.com);

� INSERT INTO Student (Student_Name,Student_Address,Email)

Values (Henry Champion, West Kent Road, HC@Yahoo.com);

� INSERT INTO Student (Student_Name,Student_Address,Email) Values (Mark Williams, China Town, MW@Yahoo.com);

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Project Report 1

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SQL Report1

� SELECT Projects_Tbl.Project_Id,Projects_Tbl.Project_Name, Employees_Tbl.Employee_No,Employees_Tbl.Employee_Name, Job_Type_Tbl.Job_Class, Job_Type_Tbl.Charges, Employee_Project_Tbl.Hours

� FROM (Projects_Tbl INNER JOIN (Employees_Tbl INNER JOIN Employee_Project_Tbl ONEmployees_Tbl.Employee_No=Employee_Project_Tbl.Emplyee_Number) ON Projects_Tbl.Project_Id=Employee_Project_Tbl.Project_id) INNER JOIN Job_Type_Tbl ON Projects_Tbl.Project_Id=Job_Type_Tbl.Project_Id;

Output report

� Try and sketch what you think the output is likely

to be

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Project Report 2

Fig: Select Query to generate the report below

Fig: Result of the query

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SQL Report 2

� SELECT Projects_Tbl.Project_Id, Projects_Tbl.Project_Name, Employees_Tbl.Employee_No, Employees_Tbl.Employee_Name, Job_Type_Tbl.Job_Class, Job_Type_Tbl.Charges, Employee_Project_Tbl.Hours, [Charges]*[hours] AS Total

� FROM (Projects_Tbl INNER JOIN (Employees_Tbl INNER JOIN Employee_Project_Tbl ON Employees_Tbl.Employee_No = Employee_Project_Tbl.Emplyee_Number) ON Projects_Tbl.Project_Id = Employee_Project_Tbl.Project_id) INNER JOIN Job_Type_Tbl ON Projects_Tbl.Project_Id = Job_Type_Tbl.Project_Id;

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Write SQL Query to implement the following two Tables. You may use MS Access Query design to help you complete this

task. The tables are based on the Project/Employee database

Table: 1

Table: 2

Try this revision task

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Joins Statements

� SQL join commands are useful when querying data from multiple tables that are linked together

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Joins Statements Cont’..

� Types of joins:� INNER JOIN (JOIN): Return rows when there is at least one match in both tables

� LEFT JOIN: Return all rows from the left table, even if there are no matches in the right table

� RIGHT JOIN: Return all rows from the right table, even if there are no matches in the left table

� FULL JOIN: Return rows when there is a match in one of the tables

� See the sites below for further details on joins:� http://infogoal.com/sql/sql-outer-join.htm

� http://www.w3schools.com/sql/sql_join_inner.asp

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Summary

� In this post, we’ve learnt that SQL is a command based language which allow database developers to create and manipulate stored record

� SQL can be used to create the database, make changes to the database and delete database objects

� SQL also help users to interact and manipulate stored data.

� Users can make a request (declare) for the data they require without the need to specify how the request should be processed

� SQL is a powerful language to learn as it is the most popular programming language for relational database applications

Next Post

� Advance SQL

Additional SQL online tutorials you!

� Introduction to SQL:

http://www.w3schools.com/sql/sql_intro.asp

EndFeel free to get in touch if you

would like to share your

thought on this topic. You can

contact me by email at:

hkwawu@aol.com