Information Systems : Fundamentals of Databasespiimt.us/piimt/module/demande/fichier/attachement_81.pdf · Information Systems : Fundamentals of ... DBMS •A Database ... Different

Information Systems : Fundamentals of Information Systems : Fundamentals of

Professor : Imade BENELALLAM

[email protected]

Information SystemPr. Imade BENELALLAM

Information Systems : Fundamentals of Information Systems : Fundamentals of DatabasesDatabases

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Objectives:

In this course, you will work with databases by :

• identifying the fundamental concepts of databases,

• creating a preliminary database design,

• applying normalization techniques,

• and familiarizing yourself with relational database management • and familiarizing yourself with relational database management systems.

you will work with MySQL by :

• Using various SQL commands, indexes, and views, you can work with and modify data efficiently within a database.

• Using features such as Enterprise Monitor and MySQL Administrator, you can manage users and administer and monitor a database.

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Outline

• Introduction to Information Systems• Fundamentals of Databases• Creating a Preliminary Database Design• Applying Normalization Techniques• Applying Normalization Techniques• Explore the MySQL RDBMS• Using the SQL Commands to Work with Tables• Working with Databases• Managing Databases• Administering a Database

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Introduction to Information Systems

Objectives : In this lesson, You will be introduced to

information systems.


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Information Systems

Definition :

Information systems or the more common legacy information systems include :

• people,

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• people,

• procedures,

• data,

• software,

• and hardware,

that are used to gather and analyze digital Data.


Types of Information Systems

The 'classic' view of Information systems is a pyramid of systems that reflected the

hierarchy of the organization, usually :

• Transaction processing systems at the bottom of the pyramid, followed by

• Management information systems,

• Decision support systems and ending with

• Executive information systems at the top.

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• Executive information systems at the top.

Fundamentals of Databases

Objectives : In this lesson, you will identify the

fundamental concepts of databases.


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Introduction : why we need a Database ?

Problem :

Imagine a scenario where you have to maintain a contact directory.

As the number of users in the directory increases, searching for the details of a

specific person or modifying his contact information becomes a cumbersome task.

Solution :

• Maintaining huge volumes of data using a data management system will enable you

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• Maintaining huge volumes of data using a data management system will enable you

to manage information efficiently.


Introduction : Manual file processing !!

Problem :

• Managing large volumes of data using manual file processing systems becomes

tedious and time consuming.

• It could result in issues such as data redundancy,

Solution :

• Acquiring knowledge on the basics of database and MySQL will enable you to add,

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• Acquiring knowledge on the basics of database and MySQL will enable you to add,

update, and maintain data using a computerized database management system.


Databases

• A database is an organized collection of data; it is used to facilitate easy storage and

retrieval of information.

• In a database, data may be grouped into a series of records, which can be further

organized into smaller segments of data called fields.

• A table is the basic storage unit of a database and it consists of rows and columns.

• The model of a database decides the way the data is organized in it.

Identify the Database Developpment Life Cycle

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• The model of a database decides the way the data is organized in it.


DBMS

• A Database Management System (DBMS) is an application program that is used to

manage electronic data.

• A user can use a DBMS to store and retrieve information in an organized manner.


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Database Models

Databases can be designed using various database models such as hierarchical,

network, and relational.


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Database Models


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Database Models


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Database Types


Databases can be broadly classified into two types. They are Online Transaction

Processing (OLTP) and Decision Support System (DSS).

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Database Types


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Tables


• A table is a set of data elements represented in vertical columns and horizontal

rows.

• A column is a field or an attribute of a table, and

• A row is a combination of column values in a table. it represents records.

• Tables are described by a set of unique characteristics and they store data of the

same type in each row.

• In a database structure, tables are also called entities and are used to create a

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• In a database structure, tables are also called entities and are used to create a

graphical representation of the database structure.


Data feilds


A data field, which is a column in a database table, can store specific data. Each data

field stored in a table defines data including numeric values, characters, date, and

time. Data fields, also referred to as attributes, are present in business forms,

spreadsheets, word processing documents, and web pages.

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Tiered architecture


Tiered architecture helps in the easy usage and maintenance of a database by

providing various views to different levels of users. With tiered architecture,

application developers can reuse specific codes or write development programs. It

facilitates the server to respond efficiently to client requests and also allows an end

user to access a database irrespective of the database design.

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Tiered architecture


Tiered architecture is predominantly of two types, two-tier and multi-tier.

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Tiered architecture


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Data warehouse


• A data warehouse is a collection of an

organization's electronically stored data.

• A data warehouse is also referred to as a

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• A data warehouse is also referred to as a

Decision Support System (DSS). It facilitates

effective data retrieval, analysis, extraction,

and transformation of data.

• A data warehouse is a business

intelligence technology.


Data dictionnary


A data dictionary, which is a centralized repository of data, defines the organization of a

database. It contains information such as the

• file format,

• structure,

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• structure,

• data meaning,

• data relationship, and their usage.

• list of files in a database,

• number of records in files, and

• the names and types of fields in records and their origin.

Data dictionaries are often hidden from users for security and safety purposes.


Database development life cycle


Database development involves five distinct phases from conception to completion in a

top-down, systematic approach.

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Quiz


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Quiz


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Quiz


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Creating a Preliminary Database Design

Objectives : In this lesson, you will creat a preliminary

database design


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Lesson introduction

Introduction

Organizations usually store and process massive amounts of data !!...

The problem :

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The problem :

If there are changes in the data storage structure after the design is implemented, it will

lead to major rework.


Lesson introduction (cont.)

Introduction

when you design a database, it is necessary to validate and understand the need and

usage of the proposed database at every stage. A clear and accurate design will play a

crucial role in creating effective databases.

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Types of information to collects

Analyze database requirements

• Conducting a database requirements analysis helps in collecting information on an

existing system to ensure that gaps, if any, are bridged in the new design.

• To design your database, you will collect information about any existing storage

systems in an organization.

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Sources of information


You can gather and collect information about database requirements from different

sources. Some of the sources are:

• data entry staff;

• department heads and managers, who analyze and view specific reports of their

departments;

• and business managers, who want reports that they are unable to retrieve from the

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• and business managers, who want reports that they are unable to retrieve from the

existing system.


Business rules


• Business rules are procedures and policies of a company that would affect the input of

data in a database.

• Business rules are translated into constraints, which are a technical limitation on how

data in a database can be stored and manipulated; they are enforced through database

design techniques.

• The constraints are then incorporated into the database design.

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• The constraints are then incorporated into the database design.

• Business rules influence the data you collect and store, and the manner in which you

define and establish relationships among tables.


How to conduct a database requirements analysis ?


Guidelines

1. Prepare a questionnaire.

2. State the purpose of the database at the beginning of each conversation to help

everyone stay focused.

3. Interview people who use the existing system and obtain information about the

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3. Interview people who use the existing system and obtain information about the

reports and forms they use frequently.

4. Collect information on forms and reports that you would need in the future.

5. Record all information about the existing system.

6. Review existing forms and reports to:

1. Determine the relevance of reports.

2. Identify the shortcomings in generating the desired reports.

3. Determine the existing business rules.

7. Identify the hardware and software requirements for the proposed system.

8. Identify the resources for the project and the overall cost of the system.


Keys

Identify key fields

• A key is a data field that ensures that each

record in a table is uniquely identified.

• A key field is used for searches while creating

reports based on the data in the table. In

addition, you can also use keys to establish

relationships among tables.

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relationships among tables.


Types of Keys

Identify key fields

Different types of keys are used to enter data correctly and uniquely identify it in a

table.

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Types of Keys

Identify key fields


table.

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Types of Keys

Identify key fields


table.

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Types of Keys

Identify key fields


table.

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Null values

Identify key fields

• A null value is the value used to indicate the absence of any data in a given field.

• A field is considered to be null, only when there is no value assigned to it or the data

for the field is unavailable. Further, a null value can be found in a field containing any

type of data. Null values are never equal to zero.

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type of data. Null values are never equal to zero.


Constraints

Identify key fields

• Constraints are conditions or validation checks that you apply when creating a

database to ensure storage of valid data. They are derived from business rules defined

during the database design.

• Constraints can be modified once they are defined and can be implemented at both

the table and column level.

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Types of Constraints

Identify key fields

Different types of constraints can be used in a database.

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Identify key fields


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Identify key fields


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Identify key fields


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Identify key fields


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Determine data fields

Identify key fields

Justin Valone, the database designer of Dazzle Florist is responsible for creating a

complete list of fields for their new database. He examines the existing reports and

creates a list of fields. He sets up a meeting with potential users of the new database,

such as the department head, to understand their expectations of the new database.

He summarizes the information and prepares a final list of fields including the

calculated fields.

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calculated fields.


How to Identify Key Fields

Identify key fields

Procedure Reference:

Identify Key Fields

To identify key fields:

1. Identify a candidate key by choosing a field or fields that do not accept duplicate and blank

values. A candidate key qualifies as a primary key.

2. Repeat step 1 until all candidate keys for the tables have been identified.

3. Identify a primary key from the list of candidate keys.

• From the list of candidate keys, choose a field that holds unique values under all

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• From the list of candidate keys, choose a field that holds unique values under all

circumstances.

• If a single field from the list of candidate keys cannot be identified as a primary key, you

can have a composite primary key, which is a combination of fields that do not accept

duplicate values.

• If a field in a table does not hold a unique value, you can add a new field as a unique

identifier.

4. Identify a foreign key by choosing a field or fields in a relational table that matches a primary

key column or columns of another table. In the current table, ensure that the data type of the

foreign key column matches the data type of the primary key column of the other table.

5. Repeat steps 3 and 4 until all primary keys and foreign keys for all the tables have been

identified.


Entities

Creat entity relationship diagrams

An entity is a database component with specific characteristics. In a database

structure, entities refer to tables and are used to create a graphical representation of

the database structure.

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Relatioships


• A relationship is a method used for linking two

tables based on the presence of a common field

found in both tables.

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found in both tables.

• Linking tables is necessary to create reports that

use data from both tables.

• By using relationships, you can link a record in

one table to a record in another table.


Types of Relatioships based on cardinality


Cardinality specifies the relationship among tables based on the number of rows in one

table related to the number of rows in another table.

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Types of Relatioships based on optionality


Optionality relationships are based on the occurrence of rows in related tables.

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Types of Relatioships based on optionality


Optionality relationships are based on the occurrence of rows in related tables.

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Entity Relatioship Diagram


• An Entity Relationship Diagram or ERD is a graphical representation of the design of a

database.

• An ERD consists of entities, key fields in each entity, and the relationships among the

entities.

• ERD is used as a blue print of the database structure. It helps validate the design with

the client requirements and convey the requirement analysis to the development team.

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Laboratory


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Applaying normalization techniques

Introduction : Applaying normalization techniques

Introduction

Problem :

If the client requirement is to generate a report based on the last names of employees

and the new design does not provide for a last name field in the employee table, then

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and the new design does not provide for a last name field in the employee table, then

the design does not meet the client requirement.

Solution :

• To avoid such situations, normalization principles are applied to the preliminary

design to ensure that data fields store data in the smallest form.

• A good design results in creating an efficient table structure.


Data anomalies

Normalize tables

• A data anomaly is data inconsistency introduced in data when rows are inserted or

updated in a table or deleted from a table.

• Duplicate entry of records, or improper relationships among tables cause data

anomaly.

• A data anomaly can be categorized as insertion anomaly, update anomaly, or

deletion anomaly based on the action that causes data inconsistency.

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deletion anomaly based on the action that causes data inconsistency.


Normalization

Normalize tables

• Normalization is a process that eliminates duplicate data and organizes tables to

increase the ease of managing and modifying data.

• Each normal form represents a set of rules; each normal form also assumes that the

requirements of the preceding forms have been met.

• Data normalization is part of the database design process and is not specific or

unique to any particular RDBMS.

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unique to any particular RDBMS.

• In normalizing your data, you usually divide large tables into smaller, easy-to-

maintain tables.


The normalization process

Normalize tables

The process of normalization involves applying different rules, called normal forms, in

a sequence to tables.

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Normalize tables



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Normalize tables



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Normalize tables



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The first normal form

Normalize tables

• The first normal form or 1NF is a rule that states that each field in a table should be

atomic.

• Atomic field means the data stored in that field is in its smallest form and

cannot be subdivided.

• This form of normalization is also known as atomic normalization.

• In addition, this rule also states that the database should contain no repeating

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• This form of normalization is also known as atomic normalization.

• In addition, this rule also states that the database should contain no repeating

groups, that is, no two fields in a table should store values that are logically

related.

• The first normal form is applied as the first step of the normalization process, and

this leads to splitting fields in a table or splitting tables.

Do example


Functional dependency

Normalize tables

Functional dependency is a relationship between two fields in a table where the value

in one field is determined by the value in the other field. Functional dependency is

represented as B is functionally dependent on A, such that each value of B is

determined by a unique value of A.

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The second normal form

Normalize tables

• The second normal form or 2NF is a rule that states that a table should be in the first

normal form and each non-primary key field should be functionally dependent on the

complete primary key.

• If the primary key consists of multiple fields, then all non-key fields should be

functionally dependent on all the fields of the primary key.

• The second normal form is usually applied to tables having a multiple-field primary

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• The second normal form is usually applied to tables having a multiple-field primary

key.

Do example


The third normal form

Normalize tables

• The third normal form or 3NF is a rule that is applied to tables in the second normal

form to remove any transitive dependency. That is, no non-key field should be

dependent on another non-key field in a table in the third normal form.

• The third normal form is usually applied to tables with single field primary keys. The

presence of repeated values in non-key fields is an indication that the table is not in

the third normal form.

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the third normal form.


The Boyce-codd normal form

Normalize tables

• The Boyce-Codd normal form (BCNF) is a type of the third normal form applied to

tables with multiple-field primary keys.

• In BCNF, tables with multiple-field primary keys do not have any non-key fields. If

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• In BCNF, tables with multiple-field primary keys do not have any non-key fields. If

there are any non-key fields that do not add to the uniqueness of a record, then such

fields are moved to another table.

• The non-key field in the non-BCNF table allows for logical inconsistencies.

• This is a rigid form of the third normal form. Not all third normal form tables meet

the Boyce-Codd requirement.


The higher normal forms

Normalize tables

• A higher normal form is a set of rules applied to tables in the third normal form to

prevent blank or multiple values in fields.

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prevent blank or multiple values in fields.

• When a table has a field that does not apply to many records, then it results in blank

values.

• Multiple values for a field are usually seen in tables in BCNF.


The higher normal forms

Normalize tables

Higher normal forms are the fourth, fifth, and domain/key normal forms :

• Fourth normal forms ensure that fields do not contain null or multiple values and

• Fifth normal forms prevent any redundant non-key fields in a table.

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• Fifth normal forms prevent any redundant non-key fields in a table.

• A domain/key normal form or DKNF is a set of rules that require that the database

should contain only domain constraints and key constraints. Domain constraint

specifies the set of permissible values for an attribute.


Quiz

Normalize tables

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Quiz

Normalize tables

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Quiz

Normalize tables

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Quiz

Normalize tables

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Quiz

Normalize tables

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Quiz

Normalize tables

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Quiz

Normalize tables

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Quiz

Normalize tables

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Quiz

Normalize tables

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Denormalization

Denormalize tables

• Denormalization is the process of allowing controlled redundancy in tables to

improve query performance. When the normalization process splits a table into two

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improve query performance. When the normalization process splits a table into two

and a database designer wants to combine the tables for performance reasons, the

tables are denormalized.


Why Denormalizing ?

Denormalize tables

• Designers choose to denormalize tables for many reasons, such as :

1. to keep similar fields together,

2. to keep table structures simple,

3. to allow null value fields in tables,

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3. to allow null value fields in tables,

4. to reduce joins, to avoid one-to-one relationships,

5. to reduce input-output overheads,

6. or to add calculated fields to tables to avoid complex algorithms.

• Denormalizing tables will prevent fragmenting the tables in a database, thereby

reducing the input-output overheads while creating reports.


How to Denormalize tables

Denormalize tables

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Quiz

Denormalize tables

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Quiz

Denormalize tables

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Laboratory

Laboratory

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Explore the MySQL RDBMS

Objectives : In this lesson, you will be introduced to

MySQL RDBMS


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MySQL


MySQL is a Relational Database Management System (RDBMS) developed and

distributed by Sun Microsystems. It enables you to store, retrieve, manage, organize, and

share your data optimally. Using MySQL, you can :


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MySQL users


• MySQL consists of various levels of users. Users may use MySQL for performing

transactions, developing an application, or writing efficient queries to recover data.

Based on usage, these users can be classified into three categories :


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Based on usage, these users can be classified into three categories :

1. End user : Retrieves data and uses it by initiating transactions

2. DB Developer : Designs and develops applications

3. DBA : Administers and maintains a database management system.

MySQL command line client


MySQL Command Line Client is an application with a command line interface. It provides

DBAs, developers, and end users an interface to connect to or disconnect from the

MySQL server.


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MySQL program categories


The MySQL Server has various program categories that enable you to operate a

database. These programs provide MySQL users with a graphical user interface.


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Laboratory

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Demonstration

Introduction

Introduction

Databases are designed to store a wide variety of organizational information. To use this

information, you first need to access the database. To do this, you must be familiar with

language used to communicate with databases. Writing a simple instruction using a

language that the database understands will enable you to access the required

information.

Using the SQL Commands to Work with Tables

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Structured Query Language


• Structured Query Language (SQL) is a computer language used to communicate with

a database.

• SQL consists of instructions that can be used to retrieve and delete information from

a database, and also to modify information in a database.

• SQL consists of three major language components:

1. Data Definition Language (DDL),


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1. Data Definition Language (DDL),

2. Data Manipulation Language (DML), and

3. Data Control Language (DCL).



• DDL is used to define a database. It includes clauses to create and eliminate tables

and views. This portion of the language is generally used by database designers.

• DML is used to modify and manipulate data within a database. DML includes

commands to update and insert data in a database, and select and delete data from


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commands to update and insert data in a database, and select and delete data from

a database. This portion of the language is generally used by developers

• DCL is used to control access of various users to the database. It includes commands

to specify users who are allowed to access database objects, or restricted from

accessing database objects. This portion of the language is generally used by DBAs.

Queries


A query is an instruction set that requests information from the tables present in a

database.


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Subqueries


• A subquery, also known as an inner query, is a query that is contained within another

query. The query that contains the subquery is known as the outer query.

• A subquery is used when the value needed by the outer query's condition is unknown.


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Data types


A data type is a classification of data into groups based on its characteristics. The

characteristics may include the number of characters that a value can contain, the kind


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characteristics may include the number of characters that a value can contain, the kind

of value it is–text or numeric, the presence of any decimal value, and the representation

of date and time value.

Data types

Structured Query LanguageUsing the SQL Commands to Work with Tables

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Data types


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Data types


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SQL Operators


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SQL Operators


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SQL Operators


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SQL Operators


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SQL Operators


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Creat statement

Creat tables using DDL commandsUsing the SQL Commands to Work with Tables

• CREATE is a SQL statement that enables creation of an object including a

database, table, view, or indexes inside an RDBMS. The CREATE keyword is always

followed by a database, view, table, or index name. This name is then followed by a

data field, data type, and constrains if any.

• The TEMPORARY keyword allows a table to be visible only to the current

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• The TEMPORARY keyword allows a table to be visible only to the current

connection. Once the connection is dropped, the table automatically drops.

Alter statement


The ALTER statement enables you to perform data modifications in an existing

database or database objects. It allows you to change an existing table structure by

performing various operations, such as adding or deleting columns, creating or

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performing various operations, such as adding or deleting columns, creating or

destroying indexes, and changing the current types of the columns.

Various types of data modification can be performed using the ALTER statement.

Alter command


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Drop command


The DROP statement is a SQL statement that enables you to remove one or more

database objects that includes a database, table, view, or indexes inside an RDBMS.

The TEMPORARY keyword allows you to drop temporary tables but does not check the

access rights or end an ongoing transaction. The IF EXISTS clause prevents an error from

occurring for tables that do not exist.

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occurring for tables that do not exist.

Describe command


The DESCRIBE statement is a SQL statement that is used to extract information about

columns in a table.

The syntax for the DESCRIBE statement is: {DESCRIBE | DESC} tbl_name [col_name |

wildcard]

In this syntax, col_name refers to the column name and wildcard defines a string

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In this syntax, col_name refers to the column name and wildcard defines a string

containing SQL “%” and “_” wildcard characters.

Help statement


The HELP statement is a SQL statement that is used to access and display online

information from the MySQL manual.

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information from the MySQL manual.

The syntax for this statement is: HELP 'search_string'. The search_string is case

insensitive and may include details such as content to be searched for or specific

keywords.

USE statement


The USE statement is a SQL statement that instructs MySQL to use a specific database as

its default database. This database remains as the default database until the end of a

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its default database. This database remains as the default database until the end of a

session or until another USE statement is issued. The syntax for the USE statement is:

USE db_name

Select statement

Modify data using DML commandsUsing the SQL Commands to Work with Tables

• The SELECT statement is a SQL statement used to retrieve information from a

database. The SELECT statement is composed of two parts

1. a SELECT clause that includes all the column names that are required in the

output, and

2. a FROM clause that contains the table name containing the columns. Additional

clauses can be added to the SELECT statement if necessary.

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clauses can be added to the SELECT statement if necessary.

• When all the columns of a table are required in the output, an asterisk (*) can be

used instead of column names.

Optional clause of select statement


The WHERE Clause

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The WHERE Clause

The WHERE clause is used to extract only those records that fulfill a specified criterion.

SQL WHERE Syntax

SELECT column_name(s)

FROM table_name

WHERE column_name operator value

Comparison operator


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Joins


• A join is a query that is used to combine values in two or more tables in a

relational database.

• It results in a temporary table called the joined table. A join connects tables by

using their key fields.

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Joins


Joins are broadly classified into two categories, inner joins and outer joins.

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Group by


GROUP BY is a clause used to select multiple columns from a table such that there

appears at least one arithmetic operation in the SELECT statement. It is used with

functions that perform specific actions on entire columns of data in a single query

and ignores NULL values unless otherwise stated.

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SELECT SU_Suppliers_SupplierID, SUM(OR_OrderQty) FROM

piimt.orders o GROUP BY SU_Suppliers_SupplierID;

Explain statement


The EXPLAIN statement is a SQL statement that is used to extract specific

information. You can use the EXPLAIN statement to either extract information

about the structure of a table or collect information about how MySQL executes a

SELECT statement by preceding the SELECT statement with the EXPLAIN keyword.

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EXPLAIN SELECT SU_Suppliers_SupplierID, SUM(OR_OrderQty) FROM piimt.orders o

GROUP BY SU_Suppliers_SupplierID;

Insert statement


The INSERT statement allows you to create one or more rows in a table by

specifying the actual values of the row or by subquerying. It also allows null values,

but if the column contains the not-null constraint, it returns an error message.

The INSERT keyword inserts new rows to the existing table, INSERT ... VALUE

inserts rows based on the explicit values specified during table creation.

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inserts rows based on the explicit values specified during table creation.

INSERT INTO Suppliers

(SU_SupplierID,SU_SupplierFirstName,SU_SupplierLastName,SU_SupplierAddr

ess1,SU_SupplierCity,SU_SupplierAddress2,SU_SupplierContactNumber,

SU_SupplierStatus) VALUES ('187','Imade','BENELALLAM','7035 Auctor,

Lane','Carson City','NV','775-555-6905','PR');

Update statement


The UPDATE statement is used to modify existing data in a database. The SET

clause is used to assign new values to the columns of a table. Like other DML

statements, this statement also uses the COMMIT statement at the end of the

query to make permanent changes to the data and prevent the rolling back of data

in case of any network failure.

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UPDATE Suppliers SET SU_SupplierCity='Rabat' WHERE

SU_SupplierID='187';

Replace statement


The REPLACE statement is used to insert new rows to an existing table. If the

primary key value of the old row in the existing table is the same as the value in

the new row, the old row is deleted before the new row is inserted. Therefore, this

statement either inserts a row, or deletes existing data from a row and updates it

with new values in a table.

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Delete statement


The DELETE statement is used to remove data from a table. The DELETE statement

uses a few optional clauses such as WHERE and ORDER BY. The WHERE clause

allows you to delete specific columns and ORDER BY allows you to delete rows in a

specific order. However, if the WHERE clause is not used, all the rows will be

removed from the table.

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DELETE FROM Suppliers WHERE SU_SupplierID='187';

Laboratory

LaboratoryUsing the SQL Commands to Work with Tables

Scenario

OGC books department wants to hire a few people on contract for a short period to

meet some urgent resource requirements. The store manager wants to store

information such as contract ID, first name, last name, and salary of contractors in the

“contractors” table. You have to ensure that each record in the table is unique, and the

table should be created based on the following requirements.

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table should be created based on the following requirements.

• contID VARCHAR(5) NOT NULL

• firstname VARCHAR(10) NOT NULL

• lastname VARCHAR(10) NOT NULL

• sal INT NOT NULL

Steps

1. Create the “contractors” table with the specified fields, and view information

on the created table structure.

2. Add a constraint to ensure the uniqueness of each record in the table.

Documents

Information Systems : Fundamentals of Databasespiimt.us/piimt/module/demande/fichier/attachement_81.pdf · Information Systems : Fundamentals of ... DBMS •A Database ... Different